Method and apparatus for recovering TOC and user information from an optical disk and using the TOC information to access user tracks

ABSTRACT

An optical disk having a diameter less than 140 mm and, a thickness of 1.2 mm±0.1 mm, with a plurality of record tracks having data recorded thereon as embossed pits representing information and exhibiting a track pitch in the range between 0.646 μm and 1.05 μm; with the tracks being divided into a lead-in area, a program area and a lead-out area. The data includes table of contents (TOC) information recorded in a plurality of sectors in at least one TOC track and user information recorded in a plurality of sectors in user tracks; with the TOC information including addresses of start sectors recorded in the user tracks. The data (both user and TOC information) is encoded in a long distance error correction code having at least eight parity symbols, and is run length limited (RLL) modulated.

This application is a division of U.S. patent application Ser. No.08/405,852, filed Mar. 17, 1995, now U.S. Pat. No. 5,715,355.

BACKGROUND OF THE INVENTION

The invention relates to a novel optical disk and, more particularly, tothat disk, to a method of recording and reading information on the diskand to apparatus for carrying out that method.

Optical disks have been used as mass storage devices for computerapplications, and such optical disks are known as CD-ROM's. The diskwhich is used as the CD-ROM is modeled after the standard compact disk(CD) that has been developed for audio applications and is basically anaudio CD with various improvements and refinements particularly adaptedfor computer applications. Using such a CD as a standard, the CD-ROM hasa data storage capacity of about 600 Mbytes. By using audio CDtechnology as its basis, the, CD-ROM and its disk drive have becomerelatively inexpensive and are quite popular.

However, since conventional audio CDs with their inherent format andstorage capacity have been adapted for CD-ROMs, it has heretofore beendifficult to improve the data storage capacity. In typical computerapplications, a capacity of 600 Mbytes has been found to beinsufficient.

Also, the data transfer rate that can be obtained from audio CDsgenerally is less than 1.4 Mbits/sec (Mbps). However, computerapplications generally require a transfer rate far in excess of 1.4Mbps; but is difficult to attain a faster transfer rate withconventional CD-ROMS.

Yet another disadvantage associated with conventional CD-ROMs, and whichis due to the fact that the audio CD format has been adapted forcomputer applications, is the relatively long access time associatedwith accessing a particular location on the disk. Typically, relativelylong strings of data are read from audio CDs, whereas computerapplications often require accessing an arbitrary location to read arelatively small amount of data therefrom. For example, accessing aparticular sector may take too much time for the CD controller toidentify which sector is being read by the optical pick-up.

A still further difficulty associated with CD-ROMs, and which also isattributed to the fact that such CD-ROMs are based upon audio CDtechnology, is the error correcting ability thereof. When audio data isreproduced from an audio CD, errors that cannot be correctednevertheless can be concealed by using interpolation based upon the highcorrelation of the audio information that is played back. However, incomputer applications, interpolation often cannot be used to concealerrors because of the low correlation of such data. Hence, the data thatis recorded on a CD-ROM must be encoded and modulated in a formexhibiting high error correcting ability. Heretofore, data has beenrecorded on a CD-ROM in a conventional cross interleave Reed-Solomoncode (CIRC) plus a so-called block completion error correction code.However, the block completion code generally takes a relatively longamount of time to decode the data, and more importantly, its errorcorrection ability is believed to be insufficient in the event thatmultiple errors are present in a block. Since two error correction code(ECC) techniques are used for a CD-ROM, whereas only one ECC techniqueis used for an audio CD (namely, the CIRC technique), a greater amountof non-data information must be recorded on the CD-ROM to effect sucherror correction, and this non-data information is referred to as“redundant” data. In an attempt to improve the error correction abilityof a CD-ROM, the amount of redundancy that must be recorded issubstantially increased.

OBJECTS OF THE INVENTION

Therefor, it is an object of the present invention to provide animproved optical disk having particular use as a CD-ROM which overcomesthe aforenoted difficulties and disadvantages associated with CD-ROMswhich have been used heretofore.

Another object of this invention is to provide an optical disk whichexhibits a higher access speed, thereby permitting quick access ofarbitrary locations, such as sectors, to be accessed quickly.

A further object of this invention is to provide an improved opticaldisk having a higher transfer rate than the transfer rate associatedwith CD-ROMs heretofore used.

A further object of this invention is to improve the storage capacity ofan optical disk, thereby making it more advantageous for use as aCD-ROM.

An additional object is to provide an improved optical disk which storesdata with reduced redundancy.

Still another object of this invention is to provide an improvedrecording format for an optical disk which enhances the error correctingability thereof.

Another object of this invention is to provide an optical disk having asubstantially improved recording density, thereby facilitating use ofthe disk as a CD-ROM.

A further object of this invention is to provide an improved opticaldisk having data recorded in sectors, with each sector having a sectorheader that it easily and rapidly read, particularly because the sectorheader is not encoded in a form which requires a substantially longamount of time before it is successfully decoded and recognized.

Various other objects, advantageous and features of the presentinvention will become readily apparent from the ensuing detaileddescription, and the novel features will be particularly pointed out inthe appended claims.

SUMMARY OF THE INVENTION

In accordance with this invention, an optical disk, a method andapparatus for recording that disk and a method and apparatus for readingdata from that disk are provided. The disk has a diameter of less than140 mm, a thickness of 1.2 mm±0.1 mm, and a plurality of record tracksexhibiting a track pitch in the range between 0.646 μm and 1.05 μm withdata recorded in those tracks as embossed pits. The tracks are dividedinto a lead-in area, a program area and a lead-out are, with table ofcontent (TOC) information being recorded in at least one TOC track inthe lead-in area and user information recorded in a plurality of usertracks in the program area. Each track is divided into sectors and theTOC information includes addresses of the start sectors of each usertrack. The data (both TOC and user information) is encoded in a longdistance error correction code having at least eight parity symbols, theencoded data being modulated and recorded on the disk. Preferably, thedata is modulated as run length limited (RLL) data.

In the preferred embodiment, the data is recorded with a linear densityin the range between 0.237 μm per bit and 0.378 μm per bit. Also, theprogram area is disposed in a portion of the disk having a radius from20 mm to 65 mm.

The format of the data advantageously permits rapid access to a desiredsector. Reduced redundancy in the recorded data and a higher storagecapacity are attained. Advantageously, the optical disk may record datahaving particular computer application, referred to computer data, orvideo and audio data, the later being compressed by the so-called MPEG(Moving Picture Image Coding Experts Group) technique. Audio data whichalso may be recorded preferably is compressed and then multiplexed withthe MPEG-compressed video data.

The error correction code used with the present invention preferably isa long distance code having at least eight parity symbols. EOCtechniques which have been used heretofore have relied upon so-calledshort distance codes in which a block of data is divided into twosub-blocks, each sub-block being associated with a number of paritysymbols, such as 4 parity symbols. It is known, however, that 4 paritysymbols may be used to correct 4 data symbols, and if 4 data symbols ineach sub-block are erroneous, the total number of 8 erroneous datasymbols can be corrected. But, if one sub-block contains 5 erroneousdata symbols, whereas the other sub-block contains 3 erroneous datasymbols, use of the short distance code may be effective to correct only4 data symbols in the one sub-block, thus permitting a total errorcorrection of 7 data symbols. But, in the long distance code, the blockof data is not sub-divided; and as a result, all 8 erroneous datasymbols, if present in the long distance coded data, can be corrected.

As another feature of this invention, the RLL code that is usedpreferably converts 8 bits of input data into 16 bits of data forrecording (referred to as 16 channel bits) with no margin bits providedbetween successive 16-bit symbols. In RLL codes used heretofore, 8 databits are converted into 14 channel bits and three margin bits areinserted between successive 14-bit symbols. Thus, the present inventionachieves a reduction in redundancy.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the present invention solely thereto, will bestunderstood in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of the preferred technique by which opticaldisks are made in accordance with the present invention;

FIG. 2 is a block diagram of apparatus incorporated in the presentinvention for reproducing data from the optical disk that has been madein accordance with the technique shown in FIG. 1;

FIG. 3 is a schematic representation of the recording areas for the diskmade by the technique shown in FIG. 1;

FIG. 4 is a schematic representation showing the recording areas of FIG.3 in greater detail;

FIG. 5 is a schematic representation of another format of the recordingareas;

FIG. 6 is a schematic representation of still another format of therecording areas;

FIG. 7 is a schematic representation of yet another format of therecording areas;

FIG. 8 is a tabular representation of a portion of the informationrecorded in the TOC region of the disk;

FIG. 9 is a tabular representation of another portion of the datarecorded in the TOC region;

FIG. 10 is a schematic representation of a sector of data recorded onthe disk;

FIGS. 11A-11E are tabular representations of different types of subcodedata that may be recorded in a sector;

FIG. 12 is a tabular representation of copyright data that may berecorded as subcode information in a sector;

FIG. 13 is a tabular representation of application ID information thatmay be recorded as the subcode information in a sector;

FIG. 14 is a tabular representation of time-code data that may berecorded as the subcode information in a sector;

FIG. 15 is a tabular representation of picture-type data that may berecorded as the subcode information in a sector;

FIG. 16 is a tabular representation of ECC type data that may beincluded in the TOC information recorded in the TOC region;

FIG. 17 is a schematic representation of one frame of error correctionencoded data, identified as a C1 code word;

FIG. 18 is a schematic representation of the long distance errorcorrection code format used with the present invention;

FIG. 19 is a schematic representation of a short distance errorcorrection code format that could be used with the present invention;

FIG. 20 is a schematic representation of the sequential order ofrearranged data symbols after those symbols have been played back fromthe disk;

FIG. 21 is a schematic representation of a sector of data that has beenerror correction encoded;

FIG. 22 is a schematic representation of a block code of errorcorrection encoded data in the long distance format;

FIG. 23 is a schematic representation of a block code of errorcorrection encoded data in the short distance format;

FIG. 24 is a schematic representation of a string of data symbolsexhibiting EFM modulation;

FIG. 25 is a flowchart explaining how margin bits are selected in theEFM modulated data shown in FIG. 24;

FIG. 26 is a block diagram of an EFM modulator that can be used toproduce the data string shown in FIG. 24;

FIG. 27 is a schematic representation of a frame of EFM modulated data;

FIG. 28 is a table which explains how margin bits are selected/inhibitedwhen forming the string of EFM data shown in FIG. 24;

FIGS. 29A-29D are explanatory waveforms which are useful inunderstanding how margin bits are selected;

FIG. 30 is a block diagram of a modulator that may be used with thepresent invention;

FIG. 31 is a block diagram of a demodulator that may be used with thepresent invention;

FIG. 32 is a block diagram of apparatus which may be used to supply datafor the recording technique shown in FIG. 1; and

FIG. 33 is a block diagram of data recovery apparatus that may be usedwith the playback apparatus shown in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention records different types of data on an opticaldisk, preferably for use as a CD-ROM but also adapted for use as adigital video disk (DVD). Such data may be file data or application datato be used by a computer, or it may comprise video data which sometimesis referred to herein as motion picture data which includes imageinformation and audio information and which preferably is compressed inaccordance with the various conventional video data compressionstandards, such as those known MPEG-1, MPEG-2, or when still videopictures are recorded, JPEG. It will be appreciated, therefore, that theinformation on the disk admits of “multimedia” applications.

Before describing the technique used to record data on the optical disk,a brief description is provided of the data itself. The physicalparameters of the optical disk used with the present invention are quitesimilar to the conventional audio CD; and for this reason, a drawingfigure of the disk is not provided. Nevertheless, it will be appreciatedthat the diameter of the disk is 140 mm or less, preferably 120 mm or135 mm. Data is recorded in tracks, and will be described in greaterdetail, having a track pitch in the range between 0.646 μm and 1.05 μm,and preferably in the range of 0.7 to 0.9 μm. Like audio CD data, thedata recorded on the optical disk is in the form of embossed pits havinga linear density in the range between 0.237 μm per bit and 0.387 μm perbit, although this range could be in the range of 0.3 μm to 0.4 μm perbit. Data is recorded in that portion of the disk having a radius from20 mm to 65 mm. The disk, whose thickness is 1.2 mm±0.1 mm, is intendedto be driven for a playback operation such that its linear velocity isin the range of 3.3 m to 5.3 m per second.

As a result of the linear density and track pitch of the disk,information is optically read from the disk by a pick-up head whichprojects a light beam of wavelength λ through a lens having a numericalaperture NA such that the projected beam exhibits a spatial frequency 1,where 1=λ/(2NA). The light source for the optical pick-up preferably isa laser beam whose wave length is λ=635 nm, this laser beam beingprojected through a lens whose numerical aperture is NA=0.52, resultingin the spatial frequency 1=611 nm.

Typical examples of the physical parameters associated with the opticaldisk are as following:

Disk diameter=120 mm.

Program area=23 mm to 58 mm.

Track pitch=0.84 μm.

Linear density=0.307 μm.

This results in a data storage capacity of 4.4 Gbytes.

One proposed structure for recording data on the optical disk is knownas the EFM Plus frame (EFM refers to eight-to-fourteen modulation). AnEFM Plus frame is formed of 85 data symbols (each symbols is a 16-bitrepresentation of an 8-bit byte) plus two synchronizing symbols thusconsisting of 87 16-bit symbols. One sector is comprised of 14×2 EFMplus frame. But, the amount of user information that is present in asector, that is, the amount of information which contains useful dataand thus excludes sector header information, error detection code (EPC)information, et cetera, is 2048 symbols. Accordingly, the efficiency ofthe EFM Plus format may be calculated as:

(2048×16)/(87×16×14×2)=0.8407.

That is, the efficiency of the EFM Plus format is approximately 84%,which means that 84% of all of the data that is recorded in a sector isuseful data. Therefore, if the storage capacity of the optical disk is4.4 Gbytes, as mentioned above, the amount of user data that can bestored on the disk is 84%×4.4 Gbytes=3.7 Gbytes.

Of course, if the track pitch is varied and/or if the linear density ofthe embossed pits is varied, the storage capacity of the disk likewiseis varied. For example, if the track pitch is on the order of about0.646 μm, the storage capacity of the disk may be on the order of about6.8 Gbytes, whereas if the track pitch is on the order of about 1.05 μm,the storage capacity is on the order of about 4.2 Gbytes. As a practicalmatter, however, the spatial frequency of the pick-up beam determinesthe minimum track pitch and minimum linear density because it isdesirable that the track pitch be no less than the spatial frequency ofthe pick-up beam and the linear density be no less than one-half thespatial frequency of the pick-up beam.

When compared to the audio CD, the linear density of the recorded dataof the optical disk used in the present invention is approximately 1.7times the linear density of the audio CD and the recorded capacity ofthe optical disk used with the present invention is approximately 5.5times the recording capacity of the audio CD. The optical disk of thepresent invention is driven to exhibit a linear velocity ofapproximately four times the linear velocity of the audio CD and thedata transfer rate of the optical disk of the present invention isapproximately 9 Mbps, which is about six times the data transfer rate ofthe audio CD.

With the foregoing in mind, reference is made to FIG. 1 which is a blockdiagram of the technique used to make an optical disk of the type thathas just been described. An input terminal 121 is supplied with userdata to be recorded, this data being formed of, for example, multiplexedvideo and audio information, title data and sub-information such as, butnot limited to, computer files, character data, graphic information, etcetera. The data supplied to input terminal 121 is produced by theapparatus shown in FIG. 32 and will be described below.

The user data is coupled to a change-over switch 124 which also isadapted to receive table of content (TOC) information supplied to theswitch from an input terminal 122 via a TOC encoder 125. The TOCinformation identifies various parameters of the disk which are used foraccurate reproduction of the user information recorded thereon; and theTOC information also includes data related to the user information perse, such as information that is helpful in rapidly accessing the userinformation recorded in particular tracks. The structure of the TOCinformation is described below.

Switch 124 selectively couples user data supplied at input terminal 121and encoded TOC data supplied at input terminal 122 to an errordetection code (EDC) adder 127. As will be described, TOC information isrecorded on one portion of the disk and user data is recorded on anotherportion; and switch 124 selects either the TOC information or the userdata at the appropriate times. As will be described below in conjunctionwith, for example, FIG. 21, the error detection code is added at the endof a sector of user data or TOC information; and adder 127 serves toproduce the error detection code after a sector of data has beenreceived and then adds the error detection code to the end of the sectorof data. In the preferred embodiment, a sector is comprised of 2048 bitsof useful data, plus parity bytes, plus sector header data, plus anumber of “reserved” bytes, plus the EDC code.

A sector header adder 128 is adapted to add a sector header to eachsector of user information supplied thereto by way of EDC adder 127. Aswill be described below in conjunction with FIG. 10, a sector headerincludes a synchronizing pattern and information useful to rapidlyidentify access the sector. Such information, particularly in sectorscontaining user data, includes subcode information which is coupled tothe sector header adder by way of a sector header encoder 129, thelatter opening to encode subcode information supplied thereto by way ofinput terminal 123. Such subcode information is generated by a suitablesource and, as will be described further below in conjunction with FIG.11, is used to provide helpful identifying and control informationrelated to the user data that is recorded on the disk. For example, thesubcode information identifies the track number in which the sectorwhich contains this subcode information is recorded, copyrightmanagement information which determines whether the data reproduced fromthe disk, such as video data, may be copied, application ID informationwhich designates the particular user-application for the data recordedin the sector, time code data which represents time information at whichthe user data is recorded, and information relating to video picturesthat may be recorded on the disk, such as the distance, or separation,between a video picture recorded in this sector and the next-followingand the next-preceding video pictures. A system controller 110 controlssector header encoder 129 to make certain that the proper subcodeinformation and other sector header information (as shown in FIG. 10) isplaced in the proper data location for proper recording in a user track.

User data, including the sector header added thereto by reason of sectorheader adder 128, is subjected to error correction encoding carried outby an ECC circuit 132 in combination with a memory 131 and a memorycontrol section 133, the latter being controlled by system controller110. An example of ECC encoding that may be used with the presentinvention, subject to modification so as to be applicable to the datarecorded on the optical data, is described in U.S. Re. Pat. No. 31,666.In one embodiment of the present invention, the ECC encoding produced bycircuit 132 is convolution coding and is described in greater detailbelow in conjunction with FIG. 17. It is sufficient for an understandingof FIG. 1 simply to point out that the ECC encoding assembles a frame ofdata bytes or symbols, referred to as a C2 code word formed of, forexample, 116 bytes or symbols, and generates C2 parity bytes as afunction of a respective data byte or symbol in a predetermined numberof C2 code words. For examples if the data bytes or symbols in each C2code word exhibit the sequence 1, 2, . . . 116, a C2 parity byte, orsymbol, may be produced by combining byte 1 from C2 code word C2 ₁ andbyte 2 from C2 ₂. Another C2 parity byte may be produced by combiningthe third byte of C2 code word C2 ₃ and the fourth byte of C2 ₄. In thismanner, the C2 parity bytes are generated by a cross-interleavetechnique; and as an example, 12 such C2 parity bytes are added to theC2 code word C2 ₁, even though such C2 parity bytes relate to data bytesincluded in other C2 words. Then, C1 parity bytes are generated for theC2 word (such as C2 ₁) to which has been added the C2 parity bytes,resulting in what is referred herein as a C1 code word (such as C1 ₁).The resultant C1 code word, consisting of 116 data bytes, plus 12 C2parity bytes, plus 8 C1 parity bytes is stored in memory 131.

The sequential order of the data bytes in the C1 code words stored inmemory 131 is rearranged by, for example, delaying the odd bytes so asto form an odd group of data bytes and an even group of data bytes.Since each group consists of only one-half of the data bytes included inthe C1 code word, an odd group of data bytes of one C1 code word iscombined with an even group of data bytes of the next-following C1 codeword, thus forming a disarranged order of bytes. This disarranged orderimproves the burst error immunity of the ECC encoded data. Thedisarranged order of the ECC-encoded bytes is supplied from memory 131to a modulator 140 which, preferably, carries out 8-to-16 modulation,although 8-to-14 (EFM) modulation could be used, if desired.

Memory controller 133 supplies to memory 131 the necessary read andwrite addresses to enable the generation of the C2 parity bytes incross-interleaved form and also to rearrange the sequential order of thedata bytes into the aforementioned disarranged order.

In the preferred embodiment of the ECC encoding technique, a longdistance code, also known as the L format, is use. The L format resultsin C1 code words that are arranged as shown in FIG. 18, describedfurther below. If desired, the ECC-encoded data may exhibit a shortdistance code or S format, such as is depicted in FIG. 19, describedbelow. Depending upon whether the L format or the S format is selected,system controller 110 controls memory controller 113 such that the readand write operations of memory 131 permit the data bytes to be ECCencoded in either the L format or the S format.

Modulator 140 serves to converts 8-bit bytes supplied thereto frommemory 131 into 16-bit symbols. Each symbol is run length limited (RLL),as will be described. It will be appreciated that, by generating 16-bitsymbols, the accumulated digital sum value (DSV), which is a function ofthe run length of the digital signal, that is, the number of consecutive0s or the number of consecutive 1s, is limited to permit the DCcomponent which is produced as a function of such consecutive 0s or 1s,to remain at or close to 0. By suppressing the DC, or lower frequencycomponent of the digital signal that is recorded, errors that otherwisewould be present when that digital signal is reproduced are minimized.

Modulator 140 thus produces a recording signal which is coupled tocutting apparatus 150. This apparatus is used to make an original diskfrom which one or more mother disks may be produced and from whichcopies may be stamped for distribution to end users. That is, suchstamped disks constitute the CD ROMs.

In one embodiment, the cutting apparatus includes an electro-opticalmodulator 151 which relies upon the so-called Pockels effect to modulatea light beam that is used to “cut” an original disk. This original diskis used by a mastering apparatus 160 to produce a master of the originaldisk. The mastering apparatus relies upon conventional techniques, suchas development and vacuum deposition, to produce a plurality of motherdisks. Such mother disks are used in stampers which ejection mold copiesthat subsequently are packaged and distributed. Blocks 171 and 172 inFIG. 1 are intended to represent the injection molding and packagingapparatus in manufacturing such disks. The completed disk is depicted asdisk 100.

The technique used to reproduce the information recorded on optical disk100 now will be described in conjunction with the block diagram shown inFIG. 2. Here, the disk is optically read by an optical pickup 212 whichprojects a light beam, such as a laser beam having the spatial frequency1=λ/2na, this beam being reflected from the disk and detected by aconventional pickup detector. The detector converts the reflected lightbeam to a corresponding electrical signal which is supplied from pickup212 to a waveform equalizer 213 and thence to a phase locked loop clockreproducing circuit 214 and to a demodulator 215. Transitions in therecovered electrical signal are used to synchronize the phase lockedloop to extract therefrom the clock signal which was used to record dataon the disk. The extracted clock is coupled to demodulator 215 whichperforms RLL demodulation that is described in greater detail below inconjunction with FIG. 31. Suffice it to say that if data is recorded ondisk 100 as 16-bit symbols, demodulator 215 demodulates each 16-bitsymbol to an 8-bit symbol or a byte.

The demodulated data reproduced from disk 100 is supplied to a ringbuffer 217. The clock signal extracted by phase locked loop clockreproducing circuit 214 also is supplied to the ring buffer to permitthe “clocking in” of the demodulated data. The demodulated data also issupplied from demodulator 215 to a sector header detector 221 whichfunctions to detect and separate the sector header from the demodulateddata.

Ring buffer 217 is coupled to an error correcting circuit 216 whichfunctions to correct errors that may be present in the data stored inthe ring buffer. For example, when data is recorded in the long distancecode formed of, for example, C1 code words, each comprised of 136symbols including 116 symbols representing data (i.e. C2 data), 12symbols representing C2 parity and 8 symbols representing C1 parity,error correcting circuit 216 first uses the C1 parity symbols to correcterrors that may be present in the C1 word. A corrected C1 word isrewritten into ring buffer 217; and then the error correcting circuituses the C2 parity symbols for further error correction. Those datasymbols which are subjected to further error correction are rewritteninto the ring buffer as corrected data. Reference is made toaforementioned U.S. Re. Pat. No. 31,666 for an example of errorcorrection.

In the event that an error in the sector header is sensed, errorcorrection circuit 216 uses the C1 parity symbols to correct the sectorheader, and the corrected sector header is rewritten into a sectorheader detector 221. Advantageously, the C2 parity symbols need not beused for sector header error correction.

As mentioned above, the input data symbols supplied four errorcorrection encoding exhibit a given sequence, but the error correctionencoded symbols are rearranged in a different sequence for recording. Inone arrangement, the odd and even symbols are separated and the oddsymbols of a C1 code word are recorded in an odd group while the evensymbols of that C1 code word are recorded in an even group.Alternatively, odd and even symbols of different C1 code words may begrouped together for recording. Still further, other sequentialarrangements may be used to record the data. During playback, errorcorrecting circuit 216 and ring buffer 217 cooperate to return therecovered data symbols to their original, given sequence. That is, thedata symbols may be thought of as being recorded in a disarranged orderand the combination of the error correcting circuit and ring bufferoperates to rearrange the order of the symbols in a C1 code word to itsparity arranged sequence.

Error corrected data stored in ring buffer 217 is coupled to errordetecting circuit 222 which uses the EDC bits added to the recorded databy EDC adder 127 (FIG. 1) to detect an uncorrected error. In the eventthat data cannot be corrected, EDC detector 222 provides a suitableindication, such as an error flag in a particular uncorrectable byte oran error flag in an uncorrectable C1 code word, and the error correcteddata, either with or without such error flags, as the case may be, iscoupled to output terminal 224.

In addition, TOC information is that is recovered from disk 100, afterbeing error corrected by error correcting circuit 216 and error detectedby EDC detector 222, is coupled to a TOC memory 223 for use incontrolling a data playback operation and for permitting rapid access touser data. The TOC information stored in memory 223, as well as sectorinformation separated from the reproduced data by sector header detector221 are coupled to a system controller 230. The system controllerresponds to user-generated instructions supplied thereto by a userinterface 231 to control disk drive 225 so as to access desired tracksand desired sectors in those tracks, thereby reproducing user datarequested by the user. For example, the TOC information stored in TOCmemory 223 may include data representing the location of the beginningof each track; and system controller 230 responds to a user-generatedrequest to access a particular track to control disk drive 225 such thatthe requested track is located and accessed. Particular identifyinginformation representing the data in the accessed track may be recoveredand supplied to system controller 230 by sector header detector 221 sothat rapid access to such data may be achieved. A further description ofthe TOC information and sector information useful for controlling thedisk driven in the manner broadly mentioned above is discussed ingreater detail below.

It will be appreciated from the ensuing discussion of FIGS. 10 and 21that sector header information that is recovered from the disk may beerror corrected by using the C1 parity symbols include in the same C1code word as the sector header. There is a high probability that anyerrors that may be present in the sector header can be corrected byusing the C1 parity symbols only. Since a C1 code word contains C2parity symbols that are generated from the data symbols included indifferent C1 code words, sector information is quickly detected quicklyby not waiting for all of the C2 parity symbols to be assembled beforecorrecting the sector header. Thus, position information of a sector,which is included in the sector header as a sector address, is detected,thus facilitating rapid access to a desired sector. This is to becompared with a conventional CD-ROM wherein second header information isinterleaved in several C1 code words, thus requiring the recovery anderror correction of all of those C1 code words before the sector headerdata can be assembled and interpreted.

FIG. 3 is a schematic representation of the manner in which therecording surface of disk 100 is divided into separate areas, referredto as the lead-in area, the program area and the lead-out area. FIG. 3also identifies the lead sector addresses of the program area and thelead-out area. In the illustrated embodiment, the sectors included inthe lead-in area exhibit negative sector addresses ending with thesector address −1 which, in hexadecimal notation is 0×FFFFFF. The sectoraddress of the first sector in the program area is identified as address0. As indicated, the length or duration of the program area is dependentupon the amount of data recorded therein and, thus, the address of thelast sector recorded in the program area is variable. It is appreciated,therefore, that the first sector address of the lead-out area isvariable and is dependent upon the length of the program area.

One embodiment of the disk configuration shown broadly in FIG. 3 isschematically illustrated in FIG. 4. Here, the TOC region, which iscomprised of one or more TOC tracks, is disposed in the lead-in areasand TOC information is recorded in sectors identified as −32 to −1.These 32 sectors of TOC information occupy a fixed position, such as asingle TOC track, in the lead-in area. The program area shown in FIG. 4is comprised of N tracks, where N is variable. The sector address of thefirst track of the program area is identified as address 0; and thetotal number of tracks included in the program area is dependent uponthe amount of information stored on the disk, and since the number ofsectors included in each track likewise is variable, the sectoraddresses of the lead sectors of tracks 2, 3, . . . N are variable. Ofcourse, the lead-out area commences after the Nth track is recorded.

In one embodiment, the data recorded on a given disk may admit ofdifferent applications. However, it is preferred that all of the datarecorded in a respective track admit of the same application.

FIG. 5 illustrates another disk configuration wherein TOC information isrecorded in the lead-in area from, for example, sector −32 to sector −1,as was the case in FIG. 4, and a copy of the TOC information is recordedin the program area. In the example shown in FIG. 5, the copy of the TOCinformation is recorded in at least one track whose lead sector is, forexample, sector number 1024. Since the size of the TOC region is fixedat 32 sectors, as will be described, the last sector of the copied TOCregion is sector 1055; and the lead sector of the next-following userdata track is identified as sector 1056. One reason for providing a copyof the TOC information in the program area is that some computerapplications do not easily recognize data recorded in sectors havingnegative addresses (such as sectors −32 to −1 of the TOC informationrecorded in the lead-in area).

Still another embodiment of the data configuration recorded on theoptical disk is illustrated in FIG. 6, wherein the TOC region isprovided in the program area at sectors 0 to 31. Here, the recording ofTOC information in the program area differs from the recording of TOCinformation in the program area of FIG. 5 in that the FIG. 6 arrangementdoes not include a copy of the TOC information. Nevertheless, since theTOC information is recorded in positive sector addresses in FIG. 6, thepossibility of misinterpretation due to the difficulty of recognizingnegative sector addresses by a computer is obviated.

In the embodiments of FIGS. 5 and 6 wherein TOC information is recordedin the program area, it is appreciated that the TOC region is segregatedfrom data files which are particularly relevant to the computer withwhich the optical disk is to be used. FIG. 7 illustrates a still furtherexample of the data configuration recorded on the optical disk andillustrates the TOC region to be located from sector address 32 tosector address 63. In this arrangement, information recorded in sectors0 to 31 is reserved for computer files that are particularly applicableto the computer system with which the optical disk is to be used. Thus,in the embodiments of FIGS. 5, 6 and 7 wherein TOC information isrecorded in the program area, such TOC information is segregated fromand, thus, does not interfere with file system data that may be recordedon the disk. Such file system data may occupy several sectors or severaltens of sectors; and since the TOC information is recorded in a fixednumber of sectors so as to occupy a fixed TOC region, there is nointerference by the TOC information with such file system data.

As mentioned above, in the preferred embodiment TOC information isrecorded in 32 sectors. Preferably, although not necessarily, eachsector is comprised of 2048 bytes and an example of the TOC informationrecorded in a TOC region is set out in the following Table 1.

TABLE 1 Table of Contents Information Field Name Bytes Disc Information2048 Track Information (1-st Track) 32 Track Information (2-nd Track) 32Track Information (3-rd Track) 32 . . . Track Information (N-th Track)32 Reserved 63488-32N TOTAL 65536

From the foregoing table, it is appreciated that the TOC informationincludes one sector dedicated to disk information, described moreparticularly with respect to Table 2, and up to 31 sectors in whichtrack information (see Table 3) is recorded. The TOC region alsoincludes a reserved area for the recording of information that may beuseful in the future. In a practical adaptation of the optical disk ofthe present invention, user information may be recorded in N trackswhere, for example, N=256. The track information which is recorded inthe TOC region relates to the data that is recorded only in acorresponding track, as will be described in conjunction with Table 3.

The data which constitutes the disk information recorded in the TOCregion is shown in the following Table 2:

TABLE 2 Disk Information Field Name Byte(s) HD-CD ID 8 Disk Type 1Reserved for Disk Size 1 Lead Out Sector Address 3 Reserved for MultiSession Parameters 20 Reserved for Writable Parameters 20 Volume Number1 Total Volume Number 1 Catalog Number 16 Reserved for Application IDStrings 8 Disk Title in English/ISO646 16 Local Language Country Code 3Length of Disk Title in Local Lan. (=N) 1 Disk Title in Local Lang. NFirst Track Number 1 No. of Track Entry 1 Reserved 1947-N TOTAL 2048

The fields which identify the disk information are described moreparticularly as follows:

HD-CD ID: This field, comprised of 8 bytes, contains a character stringthat identifies the data structure recorded on the disk, including thedata structure which is used to represent TOC information, the datastructure used to represent track information and the data structure ofa sector. For example, if the character string is “HD-CD001”, the datastructure recorded on the disk is of the type illustrated in FIG. 4, thedata structure used to represent TOC information is as shown in Table 1,the data structure used to represent track information is as shown inTables 2 and 3 and the data structure of the sectors of, for example,the user data tracks, is as shown in Table 4 (to be described).Different data structures may be identified by the character string“HD-CD002”, “HD-CD003”, etc. The particular character string which isrecorded in this field is detected by the reproducing apparatus whichpermits proper interpretation of the played back data consistent withthe sensed data structure.

Disk Type: This 1-byte data identifies the type of disk as, for example,a read only disk, a write once read many (WORM) disk or an erasable disk(such as the writable optical disk known as the “Mini” disc).

Reserved for Disk Size: This 1-byte field is used to identify the sizeof the optical disk. For example, a disk diameter of 120 millimeters maybe identified by a byte whose value is “1” a disk whose diameter is 80millimeters may be identified by a byte whose value is “2” and so on inaddition or, alternatively, this field may be used to identify thestorage capacity of the disk.

Lead Out Sector Address: This 3-byte field identifies the address of thefirst sector in the lead-out area.

Reserved for Multisession and Writable Parameters: These two-fields,each formed of 20 bytes, store information which is particularly usefulfor erasable disks or for WORM disks and is not further describedherein.

Volume Number: This 1-byte data field is used when several disksconstitute a collection of data for a particular appliation. Forexample, if the collection includes 2, 3, 4, etc. disks, this fieldidentifies which one of those disks is the present disk.

Total Volume Number: This 1-byte field identifies the total number ofdisks which constitute the collection in which the present disk isincluded.

Catalog Number: This 16-byte field is used to identify the type ofinformation or program that is recorded on the disk. Such identificationconstitutes the “catalog number” and is represented as UPC/EAN/JAN codepresently used to identify various goods.

Reserved For Application ID Strings: This 8-byte field is intended toidentify the particular user application for this disk medium. Atpresent, this field is not used.

Disk Title In English/ISO646: This 16-byte field stores the title of thedisk in the English language, as represented by the ISO646 standard.Although the actual title of the disk may be in another language, itsEnglish translation or a corresponding English identification of thattitle is recorded in this field. In other embodiments, the field maycontain a lesser or greater number of bytes so as to accommodate Englishtitles of lesser or greater length.

Local Language Country Code: This 3-byte field is intended to identifythe actual language of the title of the disk. For example, if the actualtitle of the disk is in Japanese, this field records the “local languagecountry” as Japan. If the title is in French, this field records the“local language country” as France. The code recorded in this field mayexhibit a numerical value corresponding to a particular country or,alternatively, the field may be as prescribed by the ISO3166 standard.If it is desired not to utilize this field, the character stringrecorded therein may be 0×FFFFFF.

Length of Disk Title in Local Language: This 1-byte field identifies thenumber of bytes that are used in the “Disk Title In Local Language”field (to be described) to represent the title of the disk in the locallanguage. If the actual disk title is not recorded in a language otherthan English, the “Disk Title In Local Language” field is left blank andthe numerical value of this “Length Of Disk Title In Local Language”field is 0.

Disk Title In Local Language: This N-byte field represents the actualtitle of the disk in the local language. It is expected that differentlanguages will adopt different standards to represent disk titles, andsuch local language standards are expected to be used as the datarecorded in this field. It is appreciated that the number of bytes whichconstitute this field is variable.

First Track Number: This 1-byte field identifies the number of the trackwhich constitutes the first track that contains user information. Forexample, if the TOC information is recorded in a single track, and ifthis single track is identified as track 0 in the program area, then thenumber of the track which constitutes the “First Track Number” is 1.

Number of Track Entries: This 1-byte field identifies the total numberof user tracks that are recorded. It is appreciated that if this fieldcontains a single byte, a maximum of 256 user data tracks, that is,tracks which contain user information, may be recorded.

The data recorded in the track information fields of the TOC data shownin Table 1 now will be described in conjunction with the following Table3:

TABLE 3 Track Information Field Name Byte(s) Track Number 1 ECC Type 1Speed Setting 1 Start SA 3 End SA 3 Time Code at Start Point 4 PlayingTime 4 Mastering Date & Time 7 Reserved for Application ID Strings 8TOTAL 32

The information recorded in each of the fields which constitute thetrack information of Table 3 now will be described in greater detail.

Track Number: This 1-byte field identifies the number of the trackrepresented by this track information. Since one byte is used toidentify the track number, it is appreciated that a maximum of 256 userdata tracks may be recorded. Of course, a single track number is used toidentify a respective track, and no two tracks on this disk areidentified by the same track number. Although it is preferred that thesuccessive tracks are numbered sequentially, it also is appreciatedthat, if desired, each track may be assigned a random number and thisrandom number is identified by the “Track Number” field.

ECC Type: This 1-byte data identifies the error correction code which isused to encode the user data recorded in this track. For example, theECC type may be either long distance error correction code, known as theL format, or short distance error correction code, known as the Sformat. The difference between the L format and the S format isdescribed below.

Speed Setting: This 1-byte data identifies the data transfer rate bywhich data is recovered from this track. For example, if a referencedata transfer rate is 1.4 Mbps, the “Speed Setting” field may exhibit avalue representing 1× this reference rate or 2× the reference rate or 4×the reference rate or 6× the reference rate. FIG. 8 is a tabularrepresentation of this “Speed Setting” field; and it is appreciated thatthe data transfer rate need not be an integral multiple of the referencedata transfer rate, as represented by the value “FF”. The byte value 0for this field, as shown in FIG. 8, represents that real time read-outof data is not required. It is appreciated that computer data, asopposed to, for example, video data, does not require real timeread-out. Hence, if computer data is recorded in the track identified bythe “Track Number” field in Table 3, the value of the “Speed Setting”field is set to 0.

Start and End Sector Addresses (SA): These 3-byte fields identify theaddress of the start sector of the track identified in the “TrackNumber” field and the address of the end sector of that track. Since thenumber of sectors included in a track is variable, the start and endsector addresses of a given track are not fixed. Hence, these fields areuseful when carrying out a high speed access operation of a desiredtrack.

Time Code At Start Point: This 4-byte field identifies a time code forthe start sector in the track identified by the “Track Number” field. Itwill be appreciated that if the user information represents video data,such video data may be recorded with conventional time codes and thestart sector of the track which contains such video data is recorded inthis “Time Code At Start Point” field. If time codes are not recordedwith the user information, this field may be left blank or may beprovided with no data, such as the character code 0.

Playing Time: This 4-byte data represents the overall playback time forthe program information that is recorded in the track identified by the“Track Number” field. For example, if the user information in this trackis an audio program, the playing time for this track may be on the orderof about 10 minutes. If the user information constitutes compressedvideo data, the playing time may be 2 or 3 or even up to 15 minutes.

Mastering Date and Time: This 7-byte field identifies the date and timeof creation of the master disk from which this optical disk was made.FIG. 9 is a tabular representation of this field. If desired, this fieldmay be replaced by null data represented by character code 0.

Reserved For Application ID Strings: This 8-byte field is intended tostore information representative of the particular application for whichthe data record in the track identified by the “Track Number” field isto be used. This differs slightly from the “Application ID” field inTable 2 because the Table 2 field is intended to identify the type ofapplication or use intended for the entire disk, whereas the“Application IOD” field of Table 3 simply the identifies the type or useof the data recorded in a particular track on that disk.

Referring now to FIG. 10, there is illustrated a preferred embodiment ofthe data structure of a sector of user information. TOC information alsois recorded in sectors, and the structure of such TOC sector is similar.The following Table 4 identifies the fields of the sectors shown in FIG.10.

TABLE 4 Sector Construction Field Name Byte(s) Sector Sync 4 CRC 2Subcode 5 Pos-in-Cluster 1 Address 3 Mode 1 Sub-Header 8 User Data 2048EDC 4 Reserved 12 TOTAL 2088

It is seen that a sector is comprised of a sector header which contains24-bytes arranged as shown in FIG. 10, followed by 2,048 bytes of userdata, 4-bytes of error detection code (EDC) and 12-bytes which arereserved. Preferably, a number of sectors constitute a “cluster”, and asone example, a cluster is comprised of 8 sectors or 16 sectors, as maybe determined by the preferred format.

A more detailed explanation of the different fields which constitute thesector shown in FIG. 10 now will be provided.

Sector Sync: This 4-byte field is formed of a predetermined bit patternwhich is readily detected and which is unique and distinctive from thedata pattern included in any other field of a sector. The accuratedetection of the sync pattern may be confirmed sensing errors which areinterpretated from the information reproduced from the sector. If alarge number of errors are detected continually, it is safely assumedthat the sync pattern has not been accurately sensed. Alternatively, andpreferably, the demodulator which is used to convert 16-bit symbols to8-bit bytes (or, more generally, to convert an m-bit symbol to an n-bitbyte) may include suitable conversion tables which are not operable toconvert the sync pattern to a byte. The sync pattern is assumed to bepresent when the demodulator is unable to find an n-bit byte whichcorresponds to a received m-bit symbol.

Cyclic Redundancy Code (CRC); This 2-byte field is derived from thesubcode data, the cluster position data and the sector address and modedata included in the sector header. Such CRC data is used to correcterrors that may be present in these fields.

Subcode: This 5-byte field is described below.

Cluster Position: This 1-byte field identifies the particular order inthe cluster in which this sector is located. For example, if the clusteris formed of a 8 sectors, this field identifies the particular sector asthe first, second, third, etc. sector in the cluster.

Address: This 3-byte field constitutes the unique address for thissector. Since the address is represented as 3-bytes, a maximum of 64Ksectors theoretically may be recorded. FIGS. 4-7 represent the sectoraddresses of different user data tracks.

Mode and Sub-Header. These fields are conventionally used ion CD-ROMsand the data represented here is the same as that conventionally used insuch CD-ROMs.

User Data: 2,048 bytes of information are recorded in the user datafield. For example, computer data, compressed video data, audio data andthe like may be recorded. If video data is recorded, the MPEG standardmay be used to compress that data, as described in standard ISO1381-1.

Error Detection Code: This 4-byte data is cyclic code which is added byEDC adder 127 (FIG. 1) and is used to enable the detection of anuncorrectable error in the sector.

A detailed discussion of the sub-code field now is provided inconjunction with FIGS. 11A-11E. It is appreciated that the sub-codefield is comprised of two portions: a 1-byte address portion and a4-byte data portion. The value of the address portion serves to identifythe type of data that is recorded in the data portion. For example, andas shown in FIG. 11A, if the value of the address portion is 0, null orzero data is recorded in the data portion.

If the value of the address portion is 1, as shown in FIG. 11B, the dataportion is provided with the following 1-byte information:

Track Number: This data identifies the number of the track in which thesector containing this sub-code is recorded.

Copyrighted: This byte exhibits the structure shown in FIG. 12 wherein a“1” bit represents that copying of the associated user data isprohibited and a “0” bit indicates that copyring of the associated datais permitted. The bit positions of the copyright byte identify the typeof user data for which copying is selectively prohibited or permitted.As shown in FIG. 12, the identified user data is analog video data,analog audio data, digital video data, digital audio data, and the like.For example, if the user data in this sector is digital video data andif copying of that digital video data is prohibited, the copyright bytemay appear as “00100000”.

Appliation ID: This indicates the particular application intended forthe user data that is recorded in this sector. Examples of typicalapplications are shown in FIG. 13 as computer text, video, video/audio,etc. If no data is recorded in this sector, the application ID byte maybe represented as the character 0.

ECC Type: This data indicates whether the user data is ECC encoded in,for example, the L format or the S format, as shown in FIG. 16. Othertypes of ECC codes may be represented by other values of this ECC typebyte.

If the value of the sub-code address is 2, as represented in FIG. 11C,the data portion represents time code. That is, if the user datarecorded in this sector is variable over time, as would be the case ifsuch data is video data, the time code data recorded in the sub-codefield represents time information at which the user data is recorded. Anexample of such time code data is represented in FIG. 14. It isappreciated that 2-digit BCD bits are used to represent the hour,minute, second and frame at which the user data in this sector isrecorded.

If the value of the address portion is 3, as depicted in FIG. 11D, thedata portion of the sub-code filed represents the distance from thesector in which this sub-code field is recorded to the first sector inwhich an immediately preceding I compressed video picture is recorded;and also the distance from this sector to the first sector in which thenext-following I compressed video picture is recorded. Those of ordinaryskill in the art will recognize that video data, when compressed inaccordance with the MPEG standard, may constitute an intraframe encodedvideo picture, typically known as an I picture, a predictive coded videopicture, typically known as a P picture, and a bi-directionallypredictive coded video picture, typically known as a B picture. The dataportion of the sub-code field whose address portion has the value of 3thus indicates the distances between this sector and the beginning ofthe next-preceding and next-following I pictures.

If the value of the address portion is 4, as shown in FIG. 11E, the dataportion includes 1-byte picture type, indicating whether the videopicture that is recorded in this sector is an I, P, or B picture (seeFIG. 15), and 2-byte temporal reference data which indicates thelocation in the original picture display sequence of the particularpicture that is recorded in this sector. This temporal reference data ishelpful during a playback operation because, as those of ordinary skillin the art recognize, the location of compressed B-picture data in theMPEG code sequence may be quite different from the actual location ofthat picture when the B-picture ultimately is displayed.

The ECC format which preferably is used with the present invention isthe L format. A schematic representation of an encoded “data frame” isdepicted in FIG. 17. The ECC “frame” is referred to herein as a C1 codeword and this word, when recorded, consists of a sync pattern followedby 136 data symbols. The term “symbol” is used rather than “byte”because, as will be described, the recorded “symbol” consists of 16 bits(known as channel bits), whereas a byte typically is understood toconsist of only 8 bits. It is appreciated, however, that the C1 codeword, prior to conversion from 8-bit bytes to 16-bit symbols, that is,prior to modulation of the C1 code word, nevertheless consists of theconstruction shown in FIG. 17, wherein it will be understood that theillustrated symbols are, in fact, bytes.

The manner in which the C1 code word structure is generated now will bebriefly described. 116 data bytes, or symbols, known as a C2 word, aresupplied to, for example, the ECC encoder formed of memory 131 and ECCcircuit 132 of FIG. 1. A C2 hold section is added to the C2 word,preferably by being inserted between two groups of 58 symbols, and a C1hold section is added to the end of the resultant 128 symbols. A holdsection merely reserves a location in the data stream in which paritydata subsequently is inserted. Thus, a preliminary C1 word may bethought of as being formed of a group of 58 data symbols followed by aC2 hold section followed by a group of 58 data symbols followed by a C1hold section. Then, C2 parity symbols are generated by, for example,modulo 2 addition. Preferably, one data symbol in one preliminary C1word is modulo-2 combined with a data symbol included in the next (orsecond) preliminary C1 word. If desired, further combinations may beeffected with a data symbol included in the third-following preliminaryC1 word, and so on, to produce one C2 parity symbol. The next C2 paritysymbol is produced by a similar combination of the next data symbol inthis first preliminary C1 word with respective data symbols in thenext-following preliminary C1 words. In this manner, C2 parity symbolsare generated by combining a predetermined number of data symbols of thesame predetermined number of successive preliminary C1 words. That is,if the C2 parity symbol is produced by modulo-2 combining two datawords, then one data word of the first preliminary C1 word is modulo-2combined with one data symbol in the next symbol position of thenext-following preliminary C1 word. If the C2 parity symbol is producedby combining three data symbols, then one data symbol in successivesymbol positions from each of three successive preliminary C1 words arecombined to produce the C2 parity symbol. And if the C2 parity symbol isgenerated by combining four data symbols, than one data symbol insuccessive symbol positions from each of four successive preliminary C1words are combined.

As a preferred aspect of this ECC encoding, the data symbols which arecombined occupy successive positions in the respective preliminary C1words. That is, if the data symbol in the first preliminary C1 word isthe nth data symbol, the data symbol in the second preliminary C1 wordis the (nth+1) th data symbol, the data symbol in the third preliminaryC1 word is the (n+2)th data symbol, and so on.

When 12 C2 parity symbols are generated in the manner just described,those 12 C2 parity symbols are inserted into the C2 hold section of thisfirst preliminary C1 word, thus forming a precursory C1 word. Then, 8 C1parity symbols are generated by conventional parity symbol generation inresponse to the data and parity symbols included in this precursory C1word. The generated C1 parity symbols are inserted into the C1 holdsection thus forming the C1 code word.

In the C1 code word shown in FIG. 17, the C2 parity symbols are insertedbetween two groups of data symbols. Alternatively, the C2 parity symbolsmay be located at the end of the 116 data symbols, that is, at the endof the C2 word. A preestablished number of C1 code words having thestructure shown in FIG. 17 constitute the long distance error correctionencoded data. That is, a preestablished number of the C1 code words areused as the L format ECC encoded data having the structure shown in FIG.18. As illustrated, 128 C1 code words are used, such that i=0, 1 . . .127. Each C1 code word is comprised of a sync code, or pattern, followedby 136 symbols S₀, S₁, . . . S_(j) . . . S₁₃₅, wherein j=0, 1 . . . 135.The circles shown in FIG. 18 represent the manner in which the C2 paritysymbols are generated. As has been described above, the C2 paritysymbols are generated for the C1 ₀ code word in response to the datasymbols included in code words C1 ₀, C1 ₁, . . . C1 _(r), where rrepresents the number of data symbols and that are combined to generatethe parity symbol. From FIGS. 17 and 18, it is seen that symbols S₀-S₁₂₇constitute data and C2 parity symbols, and symbols S₁₂₈-S₁₃₅ constituteC1 parity symbols. It will be appreciated that, since twelve C2 paritysymbols are recorded in a C1 code word, up to twelve data symbols can becorrected. Since these twelve data symbols are included in twelvesuccessive C1 code words, a burst error of twelve C1 code words can becorrected, which amounts to a correctable error of 12×136=1,632 symbols.

An example of the S format ECC encoding is schematically illustrated inFIG. 19. In the S format, the twelve C2 parity symbols are divided intotwo groups of six C2 parity symbols each, with one group of six C2parity symbols being added to 58 data symbols and the other group of sixC2 parity symbols being added to the next 58 data symbols. Thus, ratherthan generating the C2 parity symbols from data symbols included in 128C1 code words, the C2 parity symbols in the S format are generated formsuccessive data symbols included in 64 C1 code words having theschematic representation shown in FIG. 19. Whereas the L format permitsthe use of C2 parity symbols to correct errors in twelve C1 code words,the S format supports C2 parity correction of up to six C1 code words.Hence, the S format permits the correction of a burst error of 6×136=816symbols.

When compared to the ECC format used in, for example, CD-ROMs of typethat have been proposed heretofore, the use of the L format or S formatin accordance with the present invention permits a reduction inredundancy from about 25% of prior art CD-ROMs to about 15% in thepresent invention.

A sector formed of ECC encoded data in the L format or the S format isshown in FIG. 21 wherein the sector includes a sector header formed of24 symbols and also is comprised of eighteen C1 code words, each C1 codeword having the construction shown in FIG. 17. The last C1 code wordincluded in the sector includes four error detection code symbols aretwelve symbols that are reserved for future use. The sector headerexhibits the structure shown in FIG. 10. Nevertheless, errors that maybe present in the sector header can be corrected generally by using onlythe C1 parity symbols which are generated for that C1 code word.

As an aspect of this invention, the sequence of the symbols included ina C1 code word as recorded in a track differs from the sequence of thesymbols that are supplied for recording. That is, and with reference toFIG. 1, the sequence of the symbols supplied to modulator 140 differsfrom the sequence of symbols supplied to switch 124. By recording thedata symbols in what is referred to herein as a disarranged order, thepossibility is reduced that a burst error will destroy the data to theextent that, when reproduced, the data will not be interpretable. Inparticular, if the data represents video information, the recording ofthe data symbols in disarranged order enhances the possibility thataccurate video pictures nevertheless can be recovered even in thepresence of the burst error. FIG. 20 is a schematic representation ofthe manner in which the data symbols are disarranged for recording.

Let it may be assumed that data symbols are recorded on the disk in theorder D_(k) and let it be further assumed that each C1 code word isformed of m symbols, with n of those symbols constituting a C2 code word(i.e. 116 data symbols and 12 C2 parity symbols) and m-n of thosesymbols constituting the C1 parity symbols. The relationship among i, j,k, m and n for recording thus is:

k=m×i+2×j−m, where j<m/2

k=m×i+2×j−(m−1) where j≧m/2

If the data symbols appear on the disk in the recorded sequence D₀, D₁,D₂ . . . such data symbols are grouped into an odd group followed by aneven group. For example, and assuming 136 symbols, data symbols D₀-D₆₇constitute an odd group of odd numbered data symbols and data symbolsD₆₈-D₁₃₅ constitute an even group of even data symbols. It will beunderstood that “odd” and “even” refer to the original sequence in whichthose data symbols had been presented for recording. In the foregoingequations, i is the sequential order in which the C1 code words arepresented for recording, j is the sequential order of the m symbols ineach C1 code word presented for recording and k is the order in whichthe m symbols are recorded on the disk. That is, D_(j)≠D_(k),

When the C1 code words having data symbols in the sequence D₀, D₁, . . .D₁₃₅ are played back from the disk, the data symbols stored in ringbuffer 217 of FIG. 2 are rearranged to the sequence illustrated in FIG.20. This sequence of FIG. 20 is referred to as the arranged sequence andis formed of sequential alternating odd and even data symbols which isthe same sequence as the data symbols originally presented to switch 124of FIG. 1 for recording. It will be appreciated that the data symbolswhich are included in the recorded C1 ₁ code word in fact belong in partto C1 ₀ code word and the C1 ₁ code word. That is, if the C1 ₁ recordedcode word is formed of symbols D₀, D₁, . . . D₁₃₅, the reproduced C1 ₀code word includes symbols D₁, D₃, . . . D₁₃₃, D₁₃₅ and the reproducedC1 ₁ code word includes symbols D₀, D₂, . . . D₁₃₂, D₁₃₄. The sequentialstorage positions in ring buffer 217 of FIG. 2 of the symbols D_(k) thatare reproduced from the disk may be expressed as follows:

i=(k/m)−(kmod2)+1

j=(m/2)×(kmod2)+(kmodm)/2

where i is the sequential order of the C1 code words that are read outof the ring buffer, j is the sequential order of the sequence of the msymbols in each C1 code word that is read out of the ring buffer and kis the disarranged order in which the m symbols are recorded on thedisk.

Although the present invention preferably records data in the L formatof ECC encoding, the teachings herein may be employed with S format ECCencoding. Discrimination between the L format and S format may be madeby sensing the ECC byte in the track information field of the TOC data,such as the ECC byte shown in Table 3, or by sensing the ECC byteincluded in the subcode field shown in FIG. 11B, wherein the ECC byte ofthe subcode field may have the structure shown in FIG. 16. Anothertechnique that can be used for ECC format discrimation contemplatesusing one type of sector sync patter when L format ECC encoding is usedand another type of sector sync pattern when S format ECC encoding isused. Thus, not only is sector synchronization detected but, at the sametime, the type of ECC format is sensed.

Yet another technique for discriminating between L format and S formatECC encoding employs the addition of a discrimination bit immediatelyfollowing the sector sync pattern.

Still another technique for discriminating between the L and S ECCformats is based upon the ability of the ECC correcting circuit 216 ofFIG. 2 to operate satisfactorily. For example, if error correctionassumes that the ECC encoded data is in the L format and errorcorrection is not possible, it is highly likely that the data actuallyis in the S format. Conversely, if error correction assumes that the ECCencoded data is in the S format but error correction is not possible, itis highly likely that the data had been encoded in the L format. Thus,discrimination between the formats is dependent upon the success orfailure of error correction.

The ECC encoded data, whether in the L format or the S format,constitute convolution codes. A group of C1 code words may be thought ofas a block and such C1 code words may be block coded in the manner shownschematically in FIG. 22. Hence, in addition to L format ECC encoding,the C1 code words are block coded as will now be briefly described. Letit be assumed that the data symbols in a preliminary C1 word constitutea C2 word (as described above). Let it be assumed that the C2 words arepresented in the sequence C2 ₁, C2 ₂, C2 ₃, etc. In FIG. 22, the symbolsrepresented by an open circle are data symbols included in the C2 ₀word, the symbols represented by a filled-in circle are data symbolsincluded in the C2 ₁₆ word, the symbols represented by a triangle aredata symbols included in the C2 ₁₇ word, the symbols represented by asquare are data symbols included in the C2 ₁₈ word, and the symbolsrepresented by an X are data symbols included in the C2 ₁₉ word. Since ablock code consists of 144 C1 code words, but each C1 code word includesonly 128 data symbols (including C2 parity symbols) it follows that onedata symbol in the C1 ₁₇ code word cannot be included in the illustratedblock and is expected to be included in the next-following block.However, block coding requires all of the data symbols in a block ofcode words C1 ₀-C1 ₁₄₃ to remain in that block and, therefore, the lastdata symbol of the C1 ₁₇ code word is “folded back” into this block asthe last data symbol of the C1 ₀ code word. Similarly, the last two datasymbols of the C1 ₁₈ word are expected to fall within the next-followingblock, but because of block coding, these two symbols, identified asdata symbols 126 and 127, are folded back into the C1 ₀ and C1 ₁ codewords, respectively. Stated generally, those data symbols of a C2 wordwhich otherwise would be included in the next-following block are foldedback to the beginning of the illustrated block such that each C1 codeword included in a block of 144 C1 code words includes interleaved datasymbols from 128 of the 144 C1 code words, as shown.

Each block consists of 8 sectors, whereby a block includes more than 16Kbytes. Error correction can be carried out on a block-by-block basis.

FIG. 23 is a schematic representation of the block coding of S formatECC encoded data. The same principle that is used for the block codingof L format ECC encoded data, as discussed in conjunction with FIG. 22,is applicable to the block coding of S format ECC encoded data. Here,however, each block consists of 4 sectors; and as a result, each blockis comprised of more than 8K bytes.

The modulation technique used to modulate the C1 code words forrecording on disc 100 (e.g., the modulation technique used by modulator140 of FIG. 1) now will be described.

One type of modulation is 8-to-14 modulation (EFM) which is used as thestandard in compact discs, and one example of such EFM processing isdescribed in Japanese patent application 6-2655. In conventional EFM, an8-bit byte is converted into a 14-bit symbol (the bits of the symbolsare known as “channel” bits because they are supplied to the recordingchannel) and successive symbols are separated by margin bits. Heretoforethree margin bits were used, and these three bits were selected toassure that the Digital Sum Value (DSV) accumulated from successivesymbols is reduced. EFM is a run length limited (RLL) code and,preferably, the shortest run length permitted in EFM consists of twoconsecutive zeros which are spaced between 1s, and the longest runlength is limited to 10, wherein 10 consecutive zeros may be presentbetween 1s.

If two margin bits are used rather than 3, the possible combinations ofsuch margin bits are: 00, 01, 10 and 11. In EFM, a margin bit state 11is prohibited. Hence, only three different combinations of margin bitscan be used to link (or separate) successive symbols: 00, 01 and 10.But, depending upon the bit stream of one or the other symbols which arelinked by the margin, one or more of these possible states may beprecluded because, to use the precluded state may result in anundesirable DSV.

FIG. 24 is a schematic representation of a “string” of data symbolsseparated by margin bits. Each data symbol is comprised of 14 channelbits and the margin bits are comprised of 2 channel bits. Thus, marginbits M₁ separate data symbols D₁ and D₂; margin bits M₂ separate datasymbols D₂ and D₃; margin bits M₃ separate data symbols D₃ and D₄, andso on, with margin bits M_(m) separating data symbols D_(m) and D_(m+1).Nevertheless, assuming that the 14 channel bits included in a datasymbol are provided in 14 successive bit cells and further assuming thatthe margin bits are included in 2 successive bit cells, successive datatransitions in the string of channel bits depicted in FIG. 24 areseparated by no less than 2 data bit cells and by no more than 10 databit cells.

A string of data symbols may include parity symbols, and FIG. 27illustrates a frame of such symbols beginning with a sync pattern of 24bit cells, followed by 12 data symbols (shown as 14-bit symbolsseparated by 2 channel bits), followed by 4 parity symbols, followed by12 data symbols and ending with 4 parity symbols. The sync pattern isillustrated as a high signal level extending for 11 bit cells followedby a low signal level extending for 11 bit cells, followed by a highsignal level extending for 2 bit cells. The inverse of this pattern canbe used. FIG. 27 also depicts the two-bit margin bits which separatesuccessive data symbols; and as mentioned above, in some instances,certain ones of the three permitted combinations of margin bits cannotbe used. FIG. 28 schematically represents the conditions under which themargin bit combination 00 or the margin bit combination 01 or the marginbit combination 10 cannot be used. As will be described, a signal knownas the inhibit margin bit signal M identifies the margin bit combinationwhich cannot be used. For example, when M_(inh)=00, the margin bitcombination 00 cannot be used. Similarly, when M_(inh)=01, the marginbit combination 01 cannot be used. And when M_(inh)=10, the margin bitcombination 10 cannot be used.

Let it be assumed that margin bits separate data symbols D₁ and D₂. Letit be further assumed that the number of consecutive zeros at theleading end of data symbols D₂ is represented as A and the number ofzeros at the terminating end of data symbol D₁ is B. If A+B is equal toor exceeds 8 successive zeros (A+B≧8) then the margin bit combination 00is inhibited (M_(inh)=00).

If the most significant bit C1 of data symbols D₂ is “1” (A=0) or if thenext most significant bit C2 is “1” (A=1) or if the least significantbit C14 of data symbol D₁ is “1”, the margin bit combination 01 isinhibited (M_(inh)=01).

If the least significant bit C14 of data symbol D₁ is “1” (B=0) or ifthe next least significant bit C13 is “1” (B=1), or if the mostsignificant bit C1 of data symbol D₁ is “1”, the margin bit combination10 is inhibited (M_(inh)=10).

The foregoing 3 conditions are not mutually exclusive; and from FIG. 28it is seen that conditions may exist which preclude the margin bitcombinations 01 and 10 (both margin bit conditions are precluded if themost significant bit C1 of data symbol D₂ is “1” or if the leastsignificant bit C14 of data symbol D₁ is “1”). The number of inhibitmargin bit combinations is represented as NI. If NI=0, all three marginbit combinations may be used. If NI=1, one of the three margin bitpatterns is precluded and the other two may be used. If N=2, two of themargin bit patterns are precluded but the third is permitted. It will beappreciated that NI never is three.

Turning now to FIG. 25, there is illustrated a flow chart whichrepresents the manner in which a margin bit combination is selected forinsertion by a margin bit generator between two data symbols. At stepS1, the inhibited margin bit combinations are determined for each set ofmargin bits M₁, M₂ . . . M_(m) and the number of inhibited margin bitcombinations NI₁, NI₂, . . . MI_(m) likewise is determined. It will beappreciated that M_(inh) and NI for each set of margin bits to beinserted between data symbols may be determined from the conditionsdepicted in FIG. 28.

The flow chart then advances to inquiry S2 which determines if thenumber of inhibited combinations for the margin bit pattern M₁ is equalto 2. If so, the flow chart advances to step S3 and only a single marginbit combination can be selected. For example, if the most significantbit of data symbol D₂ is “1” NI_(I)=2 and M_(inh)=01, 10. Step S3 thuspermits only margin bit combinations 00 to be selected as the margin bitpattern M₁.

However, if inquiry S2 is answered in the negative, then two or threedifferent margin bit combinations can be selected. The flow chartadvances to step S4 where the inhibited margin bit combination M_(inh)for the n-th margin bit pattern (n72) is determined. But, if the numberof inhibited combinations for the second margin bit pattern is 2, thatis, if NI₂=2, then the n-th margin pattern is constructed as the (m+1)thmargin bit pattern. That is, if NI₂=2, only one margin bit combinationcan be selected for the remaining margin bit patterns M_(n). The flowchart then advances to step S5 wherein data symbol D₂ is linked to datasymbol D₃ which is linked to data symbol D₄ . . . to data symbol D_(n)by the respective margin bit combinations which are not inhibited.

Thereafter, in step S6, since the margin bit patterns up to M_(n) havebeen selected, and since the data symbols up to D_(n) are known, theaccumulated DSV up to D_(n) is calculated. The DSV determined for thisdata symbol simply is added to the DSV which has been accumulated fromprevious data symbols. Then, in step S7, the margin bit pattern M₁ isselected as the particular margin bit combination which minimizes theDSV that is projected to be accumulated up to data symbol D_(n).

It will be appreciated that steps S4-S7 rely upon a projected DSV; andalthough the margin bit pattern under consideration is margin patternM₁, the technique for selecting the appropriate margin bit combinationfor pattern M₁ as based upon look ahead data symbols D₂, D₃, . . .D_(n). FIG. 29 is a graphical representation of the manner in which theprojected DSV is accumulated based upon “look ahead” data symbols. Forsimplification, it is assumed that m=3, that data symbols D₁, D₂ and D₃are known, that the accumulated DSV up to data symbol D₁ is known andthat margin bit pattern M₁ is to be selected. FIG. 29A represents the14-bit data symbol, wherein a “1” is represented by a transition and a“0” is represented by no transition in the digital signal. The datasymbols shown in FIG. 29A are the same data signals used in FIGS. 29Band 29C. FIG. 29A represents the margin bit pattern M₁ as thecombination 10; FIG. 29 represents the margin bit pattern M₁ as thecombination 01 and FIG. 29C represents the margin bit pattern M₁ as thecombination 00. It is assumed that NI₁=0, meaning that there are noinhibited margin bit combinations for margin bit pattern M. It isfurther assumed that the least significant bit of a data symbol isrepresented as “CWLL” and CWLL=0 in each of data symbols D₁, D₂ and D₃.Furthermore, based upon the most significant bit of data symbol D₃,margin bit combinations 01 and 10 are inhibited (see FIG. 2) and NI₂=2.Finally, based upon the bit stream of the trailing end of data symbol D₃and the bit stream at the leading end of data symbol D₄, margin bitcombination 00 is inhibited for M₃ (see FIG. 28) and NI₃=1.

FIG. 29D illustrates the accumulated DSV that is obtained up to the endof data symbol D₃ if M₁=0, if M₁=01 and if M₁=00. In particular, curve aof FIG. 29D illustrates the accumulated DSV when M₁=10; curve brepresents the accumulated DSV when M₁=01; and curve c represents theaccumulated DSV when M₁=00. It is seen that at the end of data symbolD₂, DSV=3 if M₁=10; DSV=1 if M₁=01; and DSV=−5 if M₁=00. Thus, tominimize the accumulated DSV, the margin bit combination 01 should beselected for margin bit pattern M₁. But, if the margin bit combination01 is selected, the accumulated DSV at the end of data symbol D₃ is seento be DSV=−5. On the other hand, if the margin bit combination 00 hadbeen selected for the margin bit pattern M₁, the accumulated DSV at theend of data symbol D₃ is DSV=1. It is appreciated then, that if theprojected DSV is examined, the particular margin bit combination that isselected for margin bit pattern P₁ differs from the margin bitcombination that would be selected if the projected DSV is not examined.

FIG. 26 is a block diagram of margin bit selection apparatus in whichthe margin bit combination for margin bit pattern M₁ is determined bylooking ahead by up to m data symbols where m=4. Thus, the accumulatedDSV up to the end of data symbol D₅ is calculated. Input terminal 10 inFIG. 26 is supplied with 32 successive bytes that have been ECC encoded,and these bytes are used to read out 14-bit symbols from a conversiontable 11 stored as a ROM. Successive 14-bit symbols are coupled to anadder 13 which adds a pseudo frame sync signal to the successive datasymbols, the pseudo frame sync signal S¹ _(f) (“1XXXXXXXXXXX10”) beingadded to the leading portion of each sync frame. The pseudo frame syncsignal serves to “reserve” a location in which the actual frame syncpattern is inserted, as will be described.

Successive data symbols are coupled to registers 14-17 wherein each datasymbol is stored. Thus, register 17 stores data symbol D₁, register 16stores data symbol D₂, register 15 stores data symbol D₃, register 14stores data symbol D₄ and adder 13 now supplies data symbol D₅ to theinput of register 14. Data symbols D₄ and D₅ are coupled todiscriminator 30 which examines these data symbols to determine if anyof the bit patterns therein correspond to those shown in FIG. 28.Depending upon the sensed bit patterns, discriminator 30 generates theinhibit margin bit signal M_(inh) which precludes certain margin bitcombinations from margin bit pattern M₄. The inhibit margin bit signalproduced by the discriminator is comprised of 3 bits and is identifiedas the margin bit inhibit signal S_(inh4). A “1” in the first bitposition of S_(inh4) inhibits the margin bit combination 10, a “1” inthe second bit position of S_(inh4) inhibits the margin bit combination01 and a “1” in the third bit position of S_(inh4) inhibits the marginbit combination 00. As an example, if only the margin bit combination 00is a permitted margin bit pattern, margin bit inhibit signal S_(inh4) isrepresented as “110”.

The output of register 17 is coupled to a frame sync converter 18 whichconverts the 14-bit pseudo frame sync signal S¹ _(f) to a 24-bit framesync signal Sf. This 24-bit frame sync signal Sf is coupled toparallel-to-serial register 19. Those data symbols D₁, D₂, . . . whichare supplied successively to frame sync converter 18 are not modifiedthereby and are supplied as is, that is, in their 14-bit configuration,to the parallel-to-serial register. Register 19 converts those bitswhich are supplied thereto in parallel to serial output form. Inaddition, after a 14-bit data symbol is serially read out of theregister, a 2-bit margin pattern produced by a margin bit generator 50is serially read out of the register. Parallel-to-serial register 19 isclocked with a channel but clock having a frequency of 24.4314 MHz suchthat the serial bit output rate of register 19 is 24.4314 Mbps. Theseserial bits are modulated by an NRZI modulator 20 and coupled to anoutput 21 for recording.

The modulated NRZI serial bits also are fed back to a DSV integrator 40which integrates the DC component of such serial bits. The DSVintegrator thus accumulates the DSV of the data symbols and margin bitpatterns.

Margin bit generator 50 functions in accordance with the flow chartshown in FIG. 25 to effect the operation illustrated by the waveforms ofFIGS. 29A-29D. It is appreciated, then, that the margin bit generator 50may be a digital signal processor, an arithmetic logic unit or amicroprocessor programmed in accordance with the flow chart of FIG. 25.Thus, the appropriate margin bit combination is selected in order tominimize the accumulated DSV will obtain as a result of m subsequentdata symbols.

The foregoing has described an EFM technique in which a margin bitpattern is inserted between successive 14-bit data symbols. As a result,each 8-bit byte is converted into a 14-bit data symbol plus a 2-bitmargin pattern. A preferred embodiment of an 8-to-16 modulator whicheliminates the generation of margin bit patterns, which minimizes theaccumulated DSV and which is constrained to run length limited (2, 10)code now will be described. Referring to FIG. 30, a plurality of“fundamental conversion tables are provided, for example, fourconversion tables T₁, T₂, T₃ and T₄. Each fundamental table is comprisedof two separate tables, identified by the subscripts a and b, one ofwhich converts an 8-bit byte into a 16-bit symbol having positive DSVand the other converting the same 8-bit byte into a 16-bit symbol havingnegative DSV.

The tables are categorized as follows: if the last bit of theimmediately prceding 16-bit symbol ends as a “1” or if the last two bitsof that 16-bit symbol end as “10”, the next 16-bit symbol is selectedfrom table T_(1a) or table T_(1b), depending upon whether it isdesirable that this next selected 16-bit symbol exhibit a positive DSV(thus calling for table T_(1a)) or a negative DSV (thus calling fortable T_(1b)).

If the immediately preceding 16-bit symbol ends with two, three or foursuccessive 0s, the next-following 16-bit symbol is selected from eithertable T₂ (that is, from either table T_(2a) or table T_(2b)) or fromtable T₃ (that is, from table T_(3a) or table T_(3b)).

If the immediately preceding 16-bit symbol ends with six, seven or eightsuccessive 0s, the next-following 16-bit symbol is selected from tableT₄.

The first 16-bit symbol that is generated immediately following a framesync pattern is selected from table T₁.

The 16-bit symbols produced from tables T₂ and T₃ differ from each otherin the following important respects: all 16-bit symbols read from tableT₂ include a “0” as the first bit and a “0” as the thirteenth bit.

All 16-bit symbols read from table T₃ include a “1” as the first orthirteenth bit or a “1” as both the first and thirteenth bit.

In the 8-to-16 conversion scheme used with the present invention, it ispossible that the very same 16-bit symbol may be generated in responseto two different 8-bit bytes. However, when the 16-bit symbolrepresentative of one of these bytes is produced, the next-following16-bit symbol is produced from table T₂; whereas when the 16-bit symbolrepresentative of the other byte is produced, the next-following 16-bitsymbol is produced from table T₃. It is appreciated that, by recognizingthe table from which the next-following 16-bit symbol is produced,discrimination between the two bytes which, nevertheless, are convertedinto the same 16-bit symbol may be readily achieved.

For example, let it be assumed that an 8-bit byte having the value 10and an 8-bit byte having the value 20 both are converted to the same16-bit symbol 0010000100100100 from table T₂. But, when this 16-bitsymbol represents the byte having the value 10, the next-following16-bit symbol is produced from table T₂, whereas when the aforenoted16-bit symbol represents the byte having the value 20, thenext-following 16-bit symbol is produced from table T₃. When the symbol0010000100100100 is demodulated, it cannot be determined immediately ifthis symbol represents the byte having the value 10 or the byte havingthe value 20. But, when the next-following 16-bit symbol is examined, itis concluded that the preceding symbol 00100000100100100 represents thebyte 10 if the next-following symbol is from table T₂, and representsthe byte having the value 20 if the next-following symbol is from tableT₃. To determine whether the next-following 16-bit symbol is from tableT₂ or table T₃, the demodulator merely needs to examine the first andthirteenth bits of the next-following symbol, as discussed above.

Table T_(a) (for example, Table _(1a)) includes 16-bit symbols having aDSV which increases in the positive direction. Conversely, the 16-bitsymbols which are stored in table T_(b) have a DSV which increases inthe negative direction. As an example, if the value of an 8-bit byte isless than 64, this byte is converted into a 16-bit symbol having arelatively large DSV. Conversely, if the value of the 8-bit byte is 64or more, this byte is converted into a 16-bit symbol having a small DSV.Those 16-bit symbols which are stored in table T_(a) have positive DSVand those 16-bit symbols which are stored in table T_(b) have negativeDSV. Thus, an input byte is converted into a 16-bit symbol havingpositive or negative DSV, depending upon which table is selected forconversion, and the value of the DSV is large or small, depending uponthe value of the input byte that is converted.

The tables T_(1a), T_(1b), . . . T_(4a), T_(4b) in FIG. 30 may beconstructed as ROMs 62-69. An input to be converted is supplied from aninput terminal 61 in common to each of these ROMs. The pair of tablesT_(a), T_(b) of a fundamental table are coupled to a selector switchwhich selects one or the other table to have read out therefrom the16-bit symbol which corresponds to the input byte read out therefrom. Asshown, selector switch 71 selectively couples the output from tableT_(1a) or table T_(1b) to an input x1 of an output switch 75. Similarly,switch 72 selectively couples table T_(2a) or table T_(2b) to an inputx2 of switch 75. Switch 73 selectively couples table T_(3a) or tableT_(3b) to input x3 of switch 75. Switch 74 selectively couples tableT_(4a) or table T_(4b) to input x4 of switch 75. Output switch 75selectively couples one of its inputs x1-x4 to an output terminal 78under the control of a table selector 76. Selector switches 71-74 selecteither table T_(a) or table T_(b) under the control of a DSV calculator77. The 16-bit symbol which ultimately is supplied to output 78 also iscoupled to the table selector and to the DSV calculator, as illustrated.

Table selector 76 senses the ending bits of the 16-bit symbol suppliedfrom switch 75 to output terminal 78 to determine whether fundamentaltable T₁, T₂, T₃ or T₄ should be selected, in accordance with the tableselecting conditions discussed above. It is appreciated that the tableselector thus controls switch 75 to select the 16-bit symbol read fromthe proper fundamental table. For example, if it is assumed that the16-bit symbol supplied to output terminal 78 ends with six, seven oreight successive 0s, switch 75 is controlled by the table selector tocouple its input x4 to the output terminal such that the next-following16-bit symbol is read from fundamental table T₄. DSV calculator 77calculates the accumulated DSV, which is updated in response to each16-bit symbol supplied to output terminal 78. If the DSV increases inthe positive direction, DSV calculator 77 controls selector switches71-74 to couple the outputs from their respective tables T_(b).Conversely, if the accumulated DSV is calculated to increase in thenegative direction, selector switches 71-74 are controlled by the DSVcalculator to couple the outputs from their respectively tables T_(a).It is exposed, therefore, that if the preceding 16-bit symbol exhibits alarger negative DSV, switches 71-74 are controlled to select the next16-bit symbol having a positive DSV; and the particular table from whichthis next 16-bit symbol is read is determined by table selector 76.Thus, the accumulated DSV is seen to approach and oscillate about 0.

An example of a 16-to-8 bit converter, that is, a demodulator compatiblewith the 8-to-16 bit modulator of FIG. 30, is illustrated in FIG. 31.Here, tables are used to carry out an inverse conversion from 16-bitsymbols to 8-bit bytes and such table are identified as tables IT₁, IT₂,IT₃ and IT₄. These tables may be stored in ROMs, 84, 85, 86 and 87. Itis expected that each 8-bit byte read from a table corresponds to two16-bit symbols, one having positive DSV and the other exhibitingnegative DSV. Alternatively, if the 16-bit symbol is used as readaddress, each 8-bit byte stored in a table may have two read addresses.Stated otherwise, each 8-bit byte may be stored in two separate readaddress locations.

An input terminal 81 is supplied with a 16-bit symbol, and this symbolis stored temporarily in a register 82 and then coupled in common toinverse conversion tables IT₁-IT₄. In addition, a table selector 83 iscoupled to input terminal 81 and to the output of register 82 so that itis supplied concurrently with the presently received 16-bit symbol andthe immediately preceding 16-bit symbol. Alternatively, table selector83 may be thought of as being supplied with the presently received16-bit symbol (from the output of register 82) and the next-following16-bit symbol. The table selector is coupled to an output selectorswitch 88 which couples to output terminal 89 either conversion tableIT₁ or conversion table IT₂ or conversion table IT₃ or conversion tableIT₄.

The manner in which table selector 83 operates now will be described. Asmentioned above, the first symbol that is produced immediately followingthe frame sync pattern is read from conversion table T₁ in FIG. 30.Table selector 83 thus operates to detect the frame sync pattern so asto control output switch 88 to couple table IT₁ to output terminal 89.

If, as mentioned above, a 16-bit symbol may represent one or the otherof two different 8-bit bytes, table selector 83 senses whether thenext-following 16-bit symbol, as supplied thereto from input terminal81, is from conversion table T₂ or conversion table T₃. Thisdetermination is made by examining the first and thirteenth bits of suchnext-following 16-bit symbol. If the table selector senses that thenext-following 16-bit symbol is from table T₂, output switch 88 issuitably controlled to select the inverse conversion table whichconverts the 16-bit symbol presently provided at the output of register82 to its proper 8-bit byte. A similar operation is carried out whentable selector 83 senses that the next-following 16-bit symbol had beenread from conversion table T₃ in FIG. 30.

The present invention converts an 8-bit byte into a 16-bit symbol,whereas the prior art converts an 8-bit byte into a 14-bit symbol andinserts three margin bits between successive symbols. Consequently,since the present invention uses only 16 bits in its bit stream ascompared to the prior art use of 17 bits, the modulation technique ofthe present invention results in an effective reduction in data of16/17, or about 6%.

While the present invention is particularly applicable to a CD-ROM onwhich computer data, video data, a combination of video and audio dataor computer files may be recorded, this invention is particularly usefulin recording and reproducing digital video discs (DVD) on which videodata and its associated audio data are recorded. Such data is compressedin accordance with the MPEG standard; and when compressed video data isrecorded on the disc, the subcode information included in each sectorheader (FIG. 10) includes a subcode address having the value 3 or thevalue 4 with the resultant subcode field appearing as shown in FIG. 11Dor 11E. If the subcode address value is 3, the user data recorded in thesector conforms to the standard ISO 11172-2 (MPEG 1) or ISO 13818-2(MPEG 2). Data that is recorded in the subcode field, as shown in FIG.11D, represents the difference between the address of the sector whichcontains this subcode and the lead sector in which the previous Ipicture or next-following I picture is recorded. It is expected that anI picture (that is, an intraframe encoded picture, as mentionedpreviously) is recorded in two or more sectors. Of course, each sectorincludes a header. However, the distance data which is recorded in thesubcode field shown in FIG. 11D represents the distance to be lead, orfirst sector in which the previous I picture or next-following I pictureis recorded. If an I picture is recorded partially in one sector andpartially in another, the sector header of the “other” sector includes 0data to represent the previous I distance and the next I distance inFIG. 11D. That is, the previous I distance and the next I distance are0.

If the subcode address value is 4, the subcode field appears as shown inFIG. 11E and, as mentioned above, the picture type data indicateswhether the video data that is recorded in compressed form in thissector is I, P or B picture data and the temporal reference dataindicates the location in the sequence of pictures in which thisparticular video picture is disposed. The sector in which an I, P or Bpicture first is recorded is referred to as an I, P or B sector,respectively, even is such I, P or B picture data is recorded in atrailing portion of that sector, while other picture data is recorded ina leading portion thereof.

FIG. 32 is a block diagram of compression apparatus which is used tosupply to input terminal 121 of FIG. 1 MPEG compressed video data. Videoinformation, supplied as, for example, analog luminance (Y) and colordifference (R−Y and B−Y) signals are digitized by an analog-to-digitalconverter 101 and compressed in accordance with the MPEG compressionsystem by video compression circuitry 102. The compression system may beconsistent with the MPEG-1 standard (ISO 11172-2) or the MPEG-2 standard(ISO 13818 2). The compressed video data is stored in a buffer memory103 from which it is supplied to a multiplexor 107 for multiplexing withother data (soon to be described) which then is input to input terminal121 (FIG. 1). Information related to the compressed video data stored inbuffer memory 103 is supplied to system controller 110, this informationbeing indicative of, for example, whether the compressed video datacorresponds to an I, P or B picture, the temporal sequence of displaypictures in which this compressed video picture is located, time coderepresenting the time of receipt or time of recording of the video data,etc. The information derived from the stored, compressed video data andsupplied to the system controller is used to generate subcodeinformation that is recorded in the sector header. It is recalled fromFIG. 1 that this information is supplied from system controller 110 tosector header encoder 129 for insertion into the sector header of theuser data.

Audio signals, such as analog left-channel and right-channel signals Land R are digitized by an analog-to-digital converter 104 and compressedin an analog data compression circuit 105. This compression circuit mayoperate in accordance with the Adaptive Transform Acoustic Codingtechnique (known as ATRAC) consistent with MPEG-1 audio compression orMPEG-2 audio compression standards. It is appreciated that this ATRACtechnique presently is used to compress audio information in recordingthe medium known as the “Mini Disc” developed by Sony Corporation. Thecompressed audio data is supplied from compression circuit 105 to anaudio buffer memory 106 from which it subsequently is coupled to amultiplexor 107 for multiplexing with the compressed video data.Alternatively, compression circuit 105 can be omitted and the digitizedaudio data can be supplied directly to a buffer memory 106 as, forexample, a 16-bit PCM encoded signal. Selective information stored inthe audio buffer memory is coupled to the system controller for use ingenerating the subcode information that is recorded in the sectorheader.

Additional information, identified in FIG. 32 as sub-information,including character, computer, graphic and musical instrument fordigital interface data (MIDI) also is coupled to multiplexor 107.

Title data is generated by a character generator 111 which, for example,may be of conventional construction. The title data is identified asfill data and key data and is compressed by a compression circuit 112which encodes the title data in variable run length coding. Thecompressed title data is coupled multiplexor 107 for subsequentapplication to the input terminal 121 shown in FIG. 1.

Preferably, multiplexor 107 multiplexes the compressed video, audio andtitle data, together with the sub-information, in accordance with theMPEG-1 or MPEG-2 standard, as may be desired. The output of themultiplexor is coupled to input terminal 121 of FIG. 1 whereat themultiplexed data is ECC encoded, modulated and recorded on disc 100.

FIG. 33 is a block diagram of circuitry for recovering the video, audio,title and sub-information data that had been recorded on disc 100 andthat had been reproduced from the disc by the playback apparatus shownin FIG. 2. The input to the data recovery circuit shown in FIG. 33 isoutput terminal 224 of FIG. 2. This terminal is coupled to ademultiplexor 248 which demulitplexes the aforedescribed multiplexedvideo, audio and title data as well as the sub-information. Thedemultiplexor operates in accordance with the MPEG-1 or MPEG-2 standard,as may be desired, to separate the compressed video data, the compressedaudio data, the compressed title data and the sub-information. Thecompressed video data is stored in a buffer memory 249 from which it isexpanded in expansion circuit 250, processed in a post processor 256,for example, as may be needed to conceal errors, and reconverted back toanalog form by digital-to-analog converter 251. Expansion circuit 250operates in accordance with the MPEG-1 or MPEG-2 standard such that theoriginal video information is recovered.

Post processor 256 also is adapted to superimpose graphical titleinformation on the recovered video data, as will be described below,such that the recovered title data may be suitably displayed, as bysuperposition on a video picture.

The separated audio data is supplied from demultiplexor 248 to an audiobuffer memory 252 from which it is expanded in an expansion circuit 253and reconverted to analog form by digital-to-analog converter 254.Expansion circuit 253 operates in accordance with the MPEG-1 or MPEG-2or mini disc standard, as may be desired. If the audio data that isrecorded on disc 100 has not been compressed, expansion circuit 253 maybe omitted or bypassed.

As depicted in FIG. 33, the sub-information separated by demultiplexor248 is supplied as a direct output signal, consistent with therepresentation shown in FIG. 32 wherein such subinformation is notprocessed prior to being supplied to multiplexor 107 and no processingsubsequent to demultiplexor 248 is illustrated.

The separated title data is applied to title buffer memory 233 fromdemultiplexor 248 from which the title data is decoded by a titledecoder 260 that operates in a manner inverse to the operation ofcompression circuit 112 (FIG. 32). That is, decoder 260 may carry out aninverse variable length decoding operation. The decoded title data issupplied to post processor 256 for superposition onto the videoinformation that has been played back from the optical disc.

Demultiplexor 248 monitors the remaining capacities of buffer memories249, 252, and 233 to sense when these memories are relatively empty orfilled. The purpose of monitoring the remaining capacities of the buffermemories is to assure that data overflow therein does not occur.

System controller 230 and user interface 231 of FIG. 33 are the same assystem controller 230 and user interface 231 in FIG. 2.

While the present invention has been particularly shown and describedwith reference to preferred embodiments, it will be readily apparent tothose of ordinary skill in the art that various changes and variationsmay be made without departing from the spirit and scope of theinvention. To the extent that such variations and changes have beenmentioned herein, the appended claims are to be interpreted as includingsuch variations and changes as well as all equivalents to those featureswhich have been particularly disclosed.

What is claimed is:
 1. A method of reproducing data from an optical diskhaving a diameter less than 140 mm, a thickness of 1.2 mm±0.1 mm and arecording area divided into a lead-in area, a program area and alead-out area, and wherein said data is recorded as embossed pitsrepresenting modulated, error-correction encoded user information insectors in user tracks in said program area and representing modulated,error-correction encoded table of contents (TOC) information in sectorsin at least one TOC track in said lead-in area with said TOC informationincluding addresses of respective start sectors of said user tracks, thetracks having a track pitch in the range of 0.646 μm to 1.05 μm, saidmethod comprising the steps of rotating said disk to obtain a constantlinear velocity; projecting a pickup light beam through a lens foroptically reading the rotating disk, said pickup light beam having aspatial frequency 1=λ/2NA, where the spatial frequency 1 is less thanthe track pitch, λ is the wavelength of the pickup light beam and NA isthe numerical aperture of the lens; demodulating the data read from saiddisk; error correcting the demodulated data; separating the errorcorrected data into TOC information and user information; and using saidTOC information to access and read selected user tracks in response toaccess instructions from a user.
 2. The method of claim 1 wherein saidembossed pits have a linear density in the range between 0.237 μm perbit and 0.378 μm per bit.
 3. The method of claim 1 wherein said programarea is located in a portion of the disk having a radius of from 20 mmto 65 mm.
 4. The method of claim 1 wherein each sector of said user andTOC tracks includes a sector header at a leading portion thereof, saidsector header containing a sector sync pattern, a sector address, anerror detection code, and subcode data.
 5. The method of claim 4,wherein said subcode data in a given sector includes a subcodeidentifier and subcode information of a type identified by said subcodeidentifier.
 6. The method of claim 5 wherein said subcode identifier isa subcode address.
 7. The method of claim 5 wherein said subcodeinformation includes track identifying data which identifies the trackin which said given sector is recorded, copyright data which indicateswhether user information in said track is permitted to be copied, andapplication identifying data which identifies a predeterminedapplication allotted to said user information in said track.
 8. Themethod of claim 5 wherein said user information is picture informationrepresenting a respective picture, said picture information beingrecorded in at least one sector in a user track, and wherein saidsubcode information includes first distance information representing thedistance from said given sector to the sector in which pictureinformation representing a next preceding picture is recorded and seconddistance information representing the distance from said given sector tothe sector in which picture information representing a next followingpicture is recorded.
 9. The method of claim 8 wherein said pictureinformation is recorded in a lead sector and at least one followingsector; and each said distance information represents the distance fromsaid given sector to a next lead sector.
 10. The method of claim 9wherein said picture information is compressed picture data selectivelycomprised of intraframe encoded picture data or predictively encodedpicture data; and said first and second distance information eachrepresents the distance from said given sector to the next lead sensorin which intraframe encoded picture data is recorded.
 11. The method ofclaim 5 wherein said user information is compressed picture dataselectively comprised of different compression-encoded data representingrespective pictures having a predetermined display sequence, and saidsubcode information includes type identifying information foridentifying the type of compression-encoded data that is recorded insaid given sector and sequence information for identifying the locationin said display sequence of the picture represented by thecompression-encoded data that is recorded in said given sector.
 12. Themethod of claim 5 wherein said user information is variable over time,and said subcode information includes time code data representing timeinformation at which said user information is recorded.
 13. The methodof claim 1 wherein said TOC information is representative ofrecord/playback characteristics, diameter, recording capacity and numberof record tracks of said disk.
 14. The method of claim 13 wherein saidrecord/playback characteristics of said optical disk represent a readonly disk, a write once disk or an erasable disk.
 15. The method ofclaim 1 wherein said TOC information includes TOC identification datafor identifying a location of said at least one TOC track, dataconfiguration of said at least one TOC track, and sector configurationof each of said plurality of sectors.
 16. The method of claim 1 whereinsaid TOC information includes data representative of disk size.
 17. Themethod of claim 1 wherein said TOC information includes datarepresentative of a time code associated with said user information. 18.The method of claim 1 wherein said user information is reproducible at aselected one of plural playback speeds; and said TOC informationincludes data representative of said selected playback speed.
 19. Themethod of claim 1 wherein said error-correction encoded information isformed of a pre-established number of C1 code words, each C1 code wordcontaining information symbols, C2 parity symbols each of which isderived from an information symbol included in a preassigned number ofC1 code words, and C1 parity symbols each of which is derived from apredetermined number of symbols, including information symbols and C2parity symbols in said C1 code word; and wherein said step of errorcorrecting comprises using said C1 parity symbols to error correct theC1 code word which contains said C1 parity symbols, using said C2 paritysymbols in said C1 code word to error correct respective informationsymbols included in said preassigned number of C1 code words, andforming an error corrected C1 code word from the information symbolsthat had been corrected as a result of using said C2 parity symbols. 20.The method of claim 19 wherein said information symbols are recorded ina disarranged order, and wherein the step of error correcting furthercomprises rearranging the order of the symbols included in said errorcorrected code word to an arranged sequence.
 21. The method of claim 20wherein said disarranged order is formed of odd information symbolsrecorded in an odd group and even information symbols recorded in aneven group, and said arranged sequence is formed of sequentialalternating odd and even information symbols.
 22. The method of claim 21wherein each C1 code word is formed of m symbols including ninformational symbols, where m and n are integers; and wherein:i=(k/m)−(kmod2)+1 j=(m/2)×(kmod2)+(kmodm)/2 where i is the sequentialorder of the error-corrected C1 code words, j is the sequential order ofthe arranged sequence of m symbols in each error-corrected C1 code word,and k is the disarranged order in which the m symbols are recorded onthe disk.
 23. The method of claim 1 wherein the error correction encodeddata is in a convolution code.
 24. The method of claim 1 wherein saiddata on the disk is modulated as a run length limited (RLL) code; andsaid step of demodulating includes decoding said RLL data.
 25. Themethod of claim 24 wherein said RLL code is (2,10) RLL code, such thatsuccessive data transitions are separated by no less than 2 data bitcells and by no more than 10 data bit cells.
 26. The method of claim 24wherein said RLL code is recorded as 2n-bit information words, and saidstep of demodulating converts said 2n-bit information words into n-bitinformation words.
 27. The method of claim 26 wherein said step ofdemodulating comprises storing in each of a plurality of tables severaln-bit information words, selecting a particular table as a function of apreceding 2n-bit information word read from said disk, and reading outfrom the selected table an n-bit information word which corresponds tothe 2n-bit information word presently read from said disk.
 28. Themethod of claim 27 wherein at least one 2n-bit information word readfrom the disk corresponds to two different n-bit information words afirst of which is stored in a first table and a second of which isstored in a second table, and wherein said step of selecting furthercomprises examining the 2n-bit information word which next follows saidpresently read 2n-bit information word to select said first or saidsecond table as a function of said next-following 2n-bit informationword.
 29. The method of claim 28 wherein said step of examiningcomprises sensing predetermined bits in said next-following 2n-bitinformation word to determine the table to be selected for saidnext-following 2n-bit information word, and selecting said first or saidsecond table for said presently read 2n-bit information word dependingupon the table to be selected for said next following 2n-bit informationword.
 30. Apparatus for reproducing data from an optical disk having adiameter less than 140 mm, a thickness of 1.2 mm±0.1 mm and a recordingarea divided into a lead-in area, a program area and a lead-out area,and wherein said data is recorded as embossed pits representingmodulated, error-correction encoded information user information insectors in user tracks in said program area and representing modulated,error-correction encoded table of contents (TOC) information in sectorsin at least one TOC track in said lead-in area with said TOC informationincluding addresses of respective start sectors of said user tracks, thetracks having a track pitch in the range of 0.646 μm to 1.05 μm, saidapparatus comprising means for rotating said disk to obtain a constantlinear velocity; pickup means for projecting a pickup light beam througha lens to optically read the rotating disk, said pickup light beamhaving a spatial frequency 1=λ/2NA, where the spatial frequency 1 isless than the track pitch, λ is the wavelength of the pickup light beamand NA is the numerical aperture of the lens; demodulating means fordemodulating the data read from said disk; error correcting means forerror correcting the demodulated data; means for separating the errorcorrected data into TOC information and user information; and controlmeans responsive to said TOC information to access and read selecteduser tracks in response to access instructions from a user.
 31. Theapparatus of claim 30 wherein said embossed pits have a linear densityin the range between 0.237 μm per bit and 0.378 μm per bit.
 32. Theapparatus of claim 30 wherein said program area is located in a portionof the disk having a radius of from 20 mm to 65 mm.
 33. The apparatus ofclaim 30 wherein each sector of at least said user tracks includes asector header at a leading portion thereof, said sector headercontaining a sector sync pattern, a sector address, an error detectioncode, and subcode data.
 34. The apparatus of claim 33 wherein saidsubcode data in a given sector includes a subcode identifier and subcodeinformation of a type identified by said subcode identifier.
 35. Theapparatus of claim 34 wherein said subcode identifier is a subcodeaddress.
 36. The apparatus of claim 34 wherein said subcode informationincludes track identifying data which identifies the track in which saidgiven sector is recorded, copyright data which indicates whether userinformation in said track is permitted to be copied, and applicationidentifying data which identifies a predetermined application allottedto said user information in said track.
 37. The apparatus of claim 34wherein said user information is picture information representing arespective picture, said picture information being recorded in at leastone sector in a user track, and wherein said subcode informationincludes first distance information representing the distance from saidgiven sector to the sector in which picture information representing anext preceding picture is recorded and second distance informationrepresenting the distance from said given sector to the sector in whichpicture information representing a next following picture is recorded.38. The apparatus of claim 37 wherein said picture information isrecorded in a lead sector and at least one following sector; and eachsaid distance information represents the distance from said given sectorto a next lead sector.
 39. The apparatus of claim 38 wherein saidpicture information is compressed picture data selectively comprised ofintraframe encoded picture data or predictively encoded picture data;and said first and second distance information each represents thedistance from said given sector to the next lead sector in whichintraframe encoded picture data is recorded.
 40. The apparatus of claim34 wherein said user information is compressed picture data selectivelycomprised of different compression-encoded data representing respectivepictures having a predetermined display sequence, and said subcodeinformation includes type identifying information for identifying thetype of compression-encoded data that is recorded in said given sectorand sequence information for identifying the location in said displaysequence of the picture represented by the compression-encoded data thatis recorded in said given sector.
 41. The apparatus of claim 34 whereinsaid user information is variable over time, and said subcodeinformation includes time code data representing time information atwhich said user information is recorded.
 42. The apparatus of claim 30wherein said TOC information is representative of record/playbackcharacteristics, diameter, recording capacity and number of recordtracks of said disk.
 43. The apparatus of claim 42 wherein saidrecord/playback characteristics of said optical disk represent a readonly disk, a write once disk or an erasable disk.
 44. The apparatus ofclaim 30 wherein said TOC information includes TOC identification datafor identifying a location of said at least one TOC track, dataconfiguration of said at least one TOC track, and sector configurationof each of said plurality of sectors.
 45. The apparatus of claim 30wherein said TOC information includes data representative of disk size.46. The apparatus of claim 30 wherein said TOC information includes datarepresentative of a time code associated with said user information. 47.The apparatus of claim 30 wherein said user information is reproducibleat a selected one of plural playback speeds; and said TOC informationincludes data representative of said selected playback speed.
 48. Theapparatus of claim 30 wherein said error-correction encoded informationis formed of a pre-established number of C1 code words, each C1 codeword containing information symbols, C2 parity symbols each of which isderived from an information symbol included in a preassigned number ofC1 code words, and C1 parity symbols each of which is derived from apredetermined number of symbols, including information symbols and C2parity symbols in said C1 code word; and wherein said error correctingmeans includes C1 parity correction means to error correct a C1 codeword with C1 parity symbols included therein, C2 parity correction meansto error correct respective information symbols included in saidpreassigned number of C1 code word with C2 parity symbols included inthe error corrected C1 code word, and means for forming an errorcorrected C1 code word from the information symbols that had beencorrected by using said C2 parity correction means.
 49. The apparatus ofclaim 48 wherein said information symbols are recorded in a disarrangedorder; and wherein said error correcting means further includesrearranging means for rearranging the order of the symbols included insaid error corrected C1 code word to an arranged sequence.
 50. Theapparatus of claim 49 wherein said disarranged order is formed of oddinformation symbols recorded in an odd group and even informationsymbols recorded in an even group, and said arranged sequence is formedof sequential alternating odd and even information symbols.
 51. Theapparatus of claim 50 wherein each C1 code word is formed of m symbolsincluding n information symbols, where m and n are integers; andwherein: i=(k/m)=(kmod2)+1 j=(m/2)×(kmod2)+(kmodm)/2 where i is thesequential order of the error-corrected C1 code words, j is thesequential order of the arranged sequence of m symbols in eacherror-corrected C1 code word, and k is the disarranged order in whichthe m symbols are recorded on the disk.
 52. The apparatus of claim 30wherein the error correction encoded data is in a convolution code. 53.The apparatus of claim 30 wherein said data on the disk is modulated asa run length limited (RLL) code; and said demodulating means includes anRLL decoder.
 54. The apparatus of claim 53 wherein said RLL code is(2,10) RLL code, such that successive data transitions are separated byno less than 2 data bit cells and by no more than 10 data bit cells. 55.The apparatus of claim 53 wherein said RLL code is recorded as 2n-bitinformation words, and said RLL decoder converts said 2n-bit informationwords into n-bit information words.
 56. The apparatus of claim 55wherein said RLL decoder comprises a plurality of storage tables, eachfor storing several n-bit information words, means for selecting aparticular table as a function of a preceding 2n-bit information wordread from said disk, and means for reading out from the selected tablean n-bit information word which corresponds to the 2n-bit informationword presently read from said disk.
 57. The apparatus of claim 56wherein at least one 2n-bit information word read from the diskcorresponds to two different n-bit information words a first of which isstored in a first table and a second of which is stored in a secondtable, and wherein said means for selecting includes means for examiningthe 2n-bit information word which next follows said presently read2n-bit information word to control the selection of said first or saidsecond table as a function of said next-following 2n-bit informationword.
 58. The apparatus of claim 57 wherein said means for examiningcomprises means for sensing predetermined bits in said next-following2n-bit information word to determine the table to be selected for saidnext-following 2n-bit information word, and means for controlling saidselecting means to select said first or said second table for saidpresently read 2n-bit information word depending upon the table to beselected for said next following 2n-bit information word.
 59. A methodof reproducing data from an optical disk having a diameter less than 140mm and a recording area divided into a lead-in area, a program area anda lead-out area, and wherein said data is recorded as pits representingmodulated, error-correction encoded user information in sectors in usertracks in said program area and representing modulated, error-correctionencoded control information in sectors in at least one controlinformation region in said lead-in area or said program area with saidcontrol information including addresses of respective start sectors ofsaid user tracks, the tracks having a track pitch in the range of 0.646μm to 1.05 μm, said method comprising the steps of rotating said disk;projecting a pickup light beam through a lens for optically reading therotating disk, said pickup light beam having a spatial frequency1=λ/2NA, where the spatial frequency 1 is less than the track pitch, λis the wavelength of the pickup light beam and NA is the numericalaperture of the lens; demodulating the data read from said disk; errorcorrecting the demodulated data; separating the error corrected datainto control information and user information; and using said controlinformation to access and read selected user tracks in response toaccess instructions from a user.
 60. Apparatus for reproducing data froman optical disk having a diameter less than 140 mm and a recording areadivided into a lead-in area, a program area and a lead-out area, andwherein said data is recorded as pits representing modulated,error-correction encoded user information in sectors in user tracks insaid program area and representing modulated, error-correction encodedcontrol information in sectors in at least one control informationregion in said lead-in area or said program area with said controlinformation including addresses of respective start sectors of said usertracks, the tracks having a track pitch in the range of 0.646 μm to 1.05μm, said apparatus comprising means for rotating said disk; pickup meansfor projecting a pickup light beam through a lens for optically readingthe rotating disk, said pickup light beam having a spatial frequency1=λ/2NA, where the spatial frequency 1 is less than the track pitch, λis the wavelength of the pickup light beam and NA is the numericalaperture of the lens; demodulating means for demodulating the data readfrom said disk; error correcting means for error correcting thedemodulated data; means for separating the error corrected data intocontrol information and user information; and control means responsiveto said control information to access and read selected user tracks inresponse to access instructions from a user.
 61. A method of reproducingdata from an optical disk having a diameter less than 140 mm and arecording area divided into a lead-in area, a program area and alead-out area, and wherein said data is recorded as pits representingmodulated, error-correction encoded user information in sectors in usertracks in said program area and representing modulated, error-correctionencoded control information in sectors in at least one controlinformation region in said lead-in area or said program area with saidcontrol information, the tracks having a track pitch in the range of 0.7μm to 0.9 μm, said method comprising the steps of rotating said disk;projecting a pickup light beam through a lens for optically reading therotating disk, said pickup light beam having a spatial frequency1=λ/2NA, where the spatial frequency 1 is less than the track pitch, λis the wavelength of the pickup light beam and NA is the numericalaperture of the lens; demodulating the data read from said disk; errorcorrecting the demodulated data; and separating the error corrected datainto control information and user information.
 62. Apparatus forreproducing data from an optical disk having a diameter less than 140 mmand a recording area divided into a lead-in area, a program area and alead-out area, and wherein said data is recorded as pits representingmodulated, error-correction encoded user information in sectors in usertracks in said program area and representing modulated, error-correctionencoded control information in sectors in at least one controlinformation region in said lead-in area or said program area with saidcontrol information, the tracks having a track pitch in the range of 0.7μm to 0.9 μm, said apparatus comprising means for rotating said disk;pickup means for projecting a pickup light beam through a lens foroptically reading the rotating disk, said pickup light beam having aspatial frequency 1=λ/2NA, where the spatial frequency 1 is less thanthe track pitch, λ is the wavelength of the pickup light beam and NA isthe numerical aperture of the lens; demodulating means for demodulatingthe data read from said disk; error correcting means for correcting thedemodulated data; and means for separating the error corrected data intocontrol information and user information.